NMR systems and methods for the rapid detection of analytes

ABSTRACT

This invention features systems and methods for the detection of analytes, and their use in the treatment and diagnosis of disease.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No. 13/363,916, filed Feb. 1, 2012, which is a continuation of U.S. application Ser. No. 13/384,051, filed Jan. 13, 2012, a U.S. national phase entry of International Application No. PCT/US2011/56936, filed Oct. 19, 2011, which is a continuation-in-part of U.S. application Ser. No. 12/910,594, filed Oct. 22, 2010 and which claims benefit of U.S. Provisional Patent Application No. 61/414,141, filed Nov. 16, 2010, U.S. Provisional Patent Application No. 61/418,465, filed Dec. 1, 2010, and U.S. Provisional Patent Application No. 61/497,374, filed Jun. 15, 2011, each of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention features assays and devices for the detection of analytes, and their use in the treatment and diagnosis of disease.

Magnetic sensors have been designed to detect molecular interactions in a variety of media, including biofluids, food products, and soil samples, among other media. Upon target binding, these sensors cause changes in properties of neighboring water molecules (or any solvent molecule with free hydrogens) of a sample, which can be detected by magnetic resonance (NMR/MRI) techniques. Thus, by using these sensors in a liquid sample, it is possible to detect the presence, and potentially quantify the amount, of an analyte at very low concentration. For example, small molecules, DNA, RNA, proteins, carbohydrates, organisms, metabolites, and pathogens (e.g., viruses) can be detected using magnetic sensors.

In general, magnetic sensors are magnetic particles that bind or otherwise link to their intended molecular target to form clusters (aggregates). It is believed that when magnetic particles assemble into clusters and the effective cross sectional area becomes larger (and the cluster number density is smaller), the interactions with the water or other solvent molecules are altered, leading to a change in the measured relaxation rates (e.g., T₂, T₁, T₂*), susceptibility, frequency of precession, among other physical changes. Additionally, cluster formation can be designed to be reversible (e.g., by temperature shift, chemical cleavage, pH shift, etc.) so that “forward” or “reverse” (competitive and inhibition) assays can be developed for detection of specific analytes. Forward (clustering) and reverse (declustering) types of assays can be used to detect a wide variety of biologically relevant materials. The MRS (magnetic resonance switch) phenomenon was previously described (see U.S. Patent Publication No. 20090029392).

Many diagnostic assays require sensitivity in the picomolar or subpicomolar range. In such assays an equally low concentration of paramagnetic particles is employed. As a result, the binding events leading to cluster formation can become a rate-limiting step in the completion of the assay as the collision frequency of antigens, paramagnetic particles, and partially formed clusters is low in this concentration range (see Baudry et al., Proc Natl Acad Sci USA, 103:16076 (2006)). The current detection of infectious agents, nucleic acids, small molecules, biowarfare agents and organisms, and molecular targets (biomarkers) or the combination of molecular and immunoassay targets usually requires up-front sample preparation, time to analyze the sample, and single tests for each of the individual analytes. There is a need for a rapid, commercially-realizable NMR-based analyte detection device suitable for use with magnetic nanosensors having four unique features and qualities: 1) little to no sample preparation, 2) multiplex detection across multiple molecular types, 3) rapid acquisition of diagnostic information, and 4) accurate information for point-of-care clinical decision making.

SUMMARY OF THE INVENTION

The invention features systems and methods for the detection of analytes.

The invention features a method for detecting the presence of an analyte in a liquid sample, the method including: (a) contacting a solution with magnetic particles to produce a liquid sample including from 1×10⁶ to 1×10¹³ magnetic particles per milliliter of the liquid sample (e.g., from 1×10⁶ to 1×10⁸, 1×10⁷ to 1×10⁸, 1×10⁷ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or 1×10¹⁰ to 1×10¹³ magnetic particles per milliliter), wherein the magnetic particles have a mean diameter of from 150 nm to 699 nm (e.g., from 150 to 250, 200 to 350, 250 to 450, 300 to 500, 450 to 650, or from 500 to 699 nm), a T₂ relaxivity per particle of from 1×10⁸ to 1×10¹² mM⁻¹s⁻¹ (e.g., from 1×10⁸ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or from 1×10¹⁰ to 1×10¹² mM⁻¹s⁻¹), and binding moieties on their surface, the binding moieties operative to alter aggregation of the magnetic particles in the presence of the analyte or a multivalent binding agent; (b) placing the liquid sample in a device, the device including a support defining a well holding the liquid sample including the magnetic particles, the multivalent binding agent, and the analyte, and having an RF coil disposed about the well, the RF coil configured to detect a signal produced by exposing the liquid sample to a bias magnetic field created using one or more magnets and an RF pulse sequence; (c) exposing the sample to a bias magnetic field and an RF pulse sequence; (d) following step (c), measuring the signal; and (e) on the basis of the result of step (d), detecting the analyte. In certain embodiments, the magnetic particles are substantially monodisperse; exhibit nonspecific reversibility in the absence of the analyte and multivalent binding agent; and/or the magnetic particles further include a surface decorated with a blocking agent selected from albumin, fish skin gelatin, gamma globulin, lysozyme, casein, peptidase, and an amine-bearing moiety (e.g., amino polyethyleneglycol, glycine, ethylenediamine, or amino dextran). In particular embodiments, the liquid sample further includes a buffer, from 0.1% to 3% (w/w) albumin (e.g., from 0.1% to 0.5%, 0.3% to 0.7%, 0.5% to 1%, 0.8% to 2%, or from 1.5% to 3% (w/w) albumin), from 0.01% to 0.5% nonionic surfactant (e.g., from 0.01% to 0.05%, 0.05% to 0.1%, 0.05% to 0.2%, 0.1% to 0.3%, 0.2% to 0.4%, or from 0.3% to 0.5% nonionic surfactant), or a combination thereof. In still other embodiments, the magnetic particles include a surface decorated with 40 μg to 100 μg (e.g., 40 μg to 60 μg, 50 μg to 70 μg, 60 μg to 80 μg, or 80 μg to 100 μg,) of one or more proteins per milligram of the magnetic particles. The liquid sample can include a multivalent binding agent bearing a plurality of analytes conjugated to a polymeric scaffold. For example, the analyte can be creatinine, the liquid sample can include a multivalent binding agent bearing a plurality of creatinine conjugates, and the magnetic particles can include a surface decorated with creatinine antibodies. In another embodiment, the analyte can be tacrolimus, the liquid sample can include a multivalent binding agent bearing a plurality of tacrolimus conjugates, and the magnetic particles can include a surface decorated with tacrolimus antibodies. In particular embodiments of the method, step (d) includes measuring the T₂ relaxation response of the liquid sample, and wherein increasing agglomeration in the liquid sample produces an increase in the observed T₂ relaxation rate of the sample. In certain embodiments, the analyte is a target nucleic acid (e.g., a target nucleic acid extracted from a leukocyte, or a pathogen).

The invention features a method for detecting the presence of an analyte in a liquid sample, the method including (a) contacting a solution with magnetic particles to produce a liquid sample including from 1×10⁶ to 1×10¹³ magnetic particles per milliliter of the liquid sample (e.g., from 1×10⁶ to 1×10⁸, 1×10⁷ to 1×10⁸, 1×10⁷ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or 1×10¹⁰ to 1×10¹³ magnetic particles per milliliter), wherein the magnetic particles have a mean diameter of from 700 nm to 1200 nm (e.g., from 700 to 850, 800 to 950, 900 to 1050, or from 1000 to 1200 nm), a T₂ relaxivity per particle of from 1×10⁹ to 1×10¹² mM⁻¹s⁻¹ (e.g., from 1×10⁹ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or from 1×10¹⁰ to 1×10¹² mM⁻¹s⁻¹), and have binding moieties on their surface, the binding moieties operative to alter an aggregation of the magnetic particles in the presence of the analyte; (b) placing the liquid sample in a device, the device including a support defining a well holding the liquid sample including the magnetic particles, the multivalent binding agent, and the analyte, and having an RF coil disposed about the well, the RF coil configured to detect a signal produced by exposing the liquid sample to a bias magnetic field created using one or more magnets and an RF pulse sequence; (c) exposing the sample to a bias magnetic field and an RF pulse sequence; (d) following step (c), measuring the signal; and (e) on the basis of the result of step (d), detecting the presence or concentration of an analyte. In certain embodiments, the magnetic particles are substantially monodisperse; exhibit nonspecific reversibility in the absence of the analyte and multivalent binding agent; and/or the magnetic particles further include a surface decorated with a blocking agent selected from albumin, fish skin gelatin, gamma globulin, lysozyme, casein, peptidase, and an amine-bearing moiety (e.g., amino polyethyleneglycol, glycine, ethylenediamine, or amino dextran). In particular embodiments, the liquid sample further includes a buffer, from 0.1% to 3% (w/w) albumin (e.g., from 0.1% to 0.5%, 0.3% to 0.7%, 0.5% to 1%, 0.8% to 2%, or from 1.5% to 3% (w/w) albumin), from 0.01% to 0.5% nonionic surfactant (e.g., from 0.01% to 0.05%, 0.05% to 0.1%, 0.05% to 0.2%, 0.1% to 0.3%, 0.2% to 0.4%, or from 0.3% to 0.5% nonionic surfactant), or a combination thereof. In still other embodiments, the magnetic particles include a surface decorated with 40 μg to 100 μg (e.g., 40 μg to 60 μg, 50 μg to 70 μg, 60 μg to 80 μg, or 80 μg to 100 μg,) of one or more proteins per milligram of the magnetic particles. The liquid sample can include a multivalent binding agent bearing a plurality of analytes conjugated to a polymeric scaffold. For example, the analyte can be creatinine, the liquid sample can include a multivalent binding agent bearing a plurality of creatinine conjugates, and the magnetic particles can include a surface decorated with creatinine antibodies. In another embodiment, the analyte can be tacrolimus, the liquid sample can include a multivalent binding agent bearing a plurality of tacrolimus conjugates, and the magnetic particles can include a surface decorated with tacrolimus antibodies. In particular embodiments of the method, step (d) includes measuring the T₂ relaxation response of the liquid sample, and wherein increasing agglomeration in the liquid sample produces an increase in the observed T₂ relaxation rate of the sample. In certain embodiments, the analyte is a target nucleic acid (e.g., a target nucleic acid extracted from a leukocyte, or a pathogen).

The invention further features a method for detecting the presence of a pathogen in a whole blood sample, the method including: (a) providing a whole blood sample from a subject; (b) mixing the whole blood sample with an erythrocyte lysis agent solution to produce disrupted red blood cells; (c) following step (b), centrifuging the sample to form a supernatant and a pellet, discarding some or all of the supernatant, and resuspending the pellet to form an extract, optionally washing the pellet (e.g., with TE buffer) prior to resuspending the pellet and optionally repeating step (c); (d) lysing cells of the extract to form a lysate; (e) placing the lysate of step (d) in a detection tube and amplifying a target nucleic acid in the lysate to form an amplified lysate solution including the target nucleic acid, wherein the target nucleic acid is characteristic of the pathogen to be detected; (f) following step (e), adding to the detection tube from 1×10⁶ to 1×10¹³ magnetic particles per milliliter of the amplified lysate solution (e.g., from 1×10⁶ to 1×10⁸, 1×10⁷ to 1×10⁸, 1×10⁷ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or 1×10¹⁰ to 1×10¹³ magnetic particles per milliliter), wherein the magnetic particles have a mean diameter of from 700 nm to 1200 nm (e.g., from 700 to 850, 800 to 950, 900 to 1050, or from 1000 to 1200 nm), and binding moieties on their surface, the binding moieties operative to alter aggregation of the magnetic particles in the presence of the target nucleic acid or a multivalent binding agent; (g) placing the detection tube in a device, the device including a support defining a well for holding the detection tube including the magnetic particles and the target nucleic acid, and having an RF coil disposed about the well, the RF coil configured to detect a signal produced by exposing the liquid sample to a bias magnetic field created using one or more magnets and an RF pulse sequence; (h) exposing the sample to a bias magnetic field and an RF pulse sequence; (i) following step (h), measuring the signal from the detection tube; and (j) on the basis of the result of step (i), detecting the pathogen. In certain embodiments, steps (a) through (i) are completed within 4 hours (e.g., within 3.5 hours, 3.0 hours, 2.5 hours, 2 hours, 1.5 hours, or 1 hour). In another embodiment, step (i) is carried out without any prior purification of the amplified lysate solution (i.e., the lysate solution is unfractionated after it is formed). In particular embodiments, step c includes washing the pellet prior to resuspending the pellet to form the extract. In particular embodiments step (d) includes combining the extract with beads to form a mixture and agitating the mixture to form a lysate. The magnetic particles can include one or more populations having a first probe and a second probe conjugated to their surface, the first probe operative to bind to a first segment of the target nucleic acid and the second probe operative to bind to a second segment of the target nucleic acid, wherein the magnetic particles form aggregates in the presence of the target nucleic acid. Alternatively, the assay can be a disaggregation assay in which the magnetic particles include a first population having a first binding moiety on their surface and a second population having a second binding moiety on their surface, and the multivalent binding moiety including a first probe and a second probe, the first probe operative to bind to the first binding moiety and the second probe operative to bind to a second binding moiety, the binding moieties and multivalent binding moiety operative to alter an aggregation of the magnetic particles in the presence of the target nucleic acid. In certain embodiments, the magnetic particles are substantially monodisperse; exhibit nonspecific reversibility in the absence of the analyte and multivalent binding agent; and/or the magnetic particles further include a surface decorated with a blocking agent selected from albumin, fish skin gelatin, gamma globulin, lysozyme, casein, peptidase, and an amine-bearing moiety (e.g., amino polyethyleneglycol, glycine, ethylenediamine, or amino dextran). In particular embodiments, the lysate further includes a buffer, from 0.1% to 3% (w/w) albumin (e.g., from 0.1% to 0.5%, 0.3% to 0.7%, 0.5% to 1%, 0.8% to 2%, or from 1.5% to 3% (w/w) albumin), from 0.01% to 0.5% nonionic surfactant (e.g., from 0.01% to 0.05%, 0.05% to 0.1%, 0.05% to 0.2%, 0.1% to 0.3%, 0.2% to 0.4%, or from 0.3% to 0.5% nonionic surfactant), or a combination thereof. In still other embodiments, the magnetic particles include a surface decorated with 40 μg to 100 μg (e.g., 40 μg to 60 μg, 50 μg to 70 μg, 60 μg to 80 μg, or 80 μg to 100 μg,) of one or more proteins per milligram of the magnetic particles. The lysate can include a multivalent binding agent bearing a plurality of analytes conjugated to a polymeric scaffold.

The invention features a method for detecting the presence of a target nucleic acid in a whole blood sample, the method including: (a) providing one or more cells from a whole blood sample from a subject; (b) lysing the cells to form a lysate; (c) amplifying a target nucleic acid in the lysate to form an amplified lysate solution comprising the target nucleic acid; (d) following step (c), adding to a detection tube the amplified lysate solution and from 1×10⁶ to 1×10¹³ magnetic particles per milliliter of the amplified lysate solution, wherein the magnetic particles have a mean diameter of from 700 nm to 1200 nm and binding moieties on their surface, the binding moieties operative to alter aggregation of the magnetic particles in the presence of the target nucleic acid or a multivalent binding agent; (e) placing the detection tube in a device, the device including a support defining a well for holding the detection tube including the magnetic particles and the target nucleic acid, and having an RF coil disposed about the well, the RF coil configured to detect a signal produced by exposing the liquid sample to a bias magnetic field created using one or more magnets and an RF pulse sequence; (f) exposing the sample to a bias magnetic field and an RF pulse sequence; (h) following step (f), measuring the signal from the detection tube; and (i) on the basis of the result of step (h), detecting the target nucleic acid. In particular embodiments, the target nucleic acid is purified prior to step (d). In particular embodiments, step (b) includes combining the extract with beads to form a mixture and agitating the mixture to form a lysate. The magnetic particles can include one or more populations having a first probe and a second probe conjugated to their surface, the first probe operative to bind to a first segment of the target nucleic acid and the second probe operative to bind to a second segment of the target nucleic acid, wherein the magnetic particles form aggregates in the presence of the target nucleic acid. Alternatively, the assay can be a disaggregation assay in which the magnetic particles include a first population having a first binding moiety on their surface and a second population having a second binding moiety on their surface, and the multivalent binding moiety including a first probe and a second probe, the first probe operative to bind to the first binding moiety and the second probe operative to bind to a second binding moiety, the binding moieties and multivalent binding moiety operative to alter an aggregation of the magnetic particles in the presence of the target nucleic acid. In certain embodiments, the magnetic particles are substantially monodisperse; exhibit nonspecific reversibility in the absence of the analyte and multivalent binding agent; and/or the magnetic particles further include a surface decorated with a blocking agent selected from albumin, fish skin gelatin, gamma globulin, lysozyme, casein, peptidase, and an amine-bearing moiety (e.g., amino polyethyleneglycol, glycine, ethylenediamine, or amino dextran). In particular embodiments, the lysate further includes a buffer, from 0.1% to 3% (w/w) albumin (e.g., from 0.1% to 0.5%, 0.3% to 0.7%, 0.5% to 1%, 0.8% to 2%, or from 1.5% to 3% (w/w) albumin), from 0.01% to 0.5% nonionic surfactant (e.g., from 0.01% to 0.05%, 0.05% to 0.1%, 0.05% to 0.2%, 0.1% to 0.3%, 0.2% to 0.4%, or from 0.3% to 0.5% nonionic surfactant), or a combination thereof. In still other embodiments, the magnetic particles optionally include a surface decorated with 40 μg to 100 μg (e.g., 40 μg to 60 μg, 50 μg to 70 μg, 60 μg to 80 μg, or 80 μg to 100 μg,) of one or more proteins per milligram of the magnetic particles. The lysate can include a multivalent binding agent bearing a plurality of analytes conjugated to a polymeric scaffold.

The invention further features a method for detecting the presence of a target nucleic acid in a whole blood sample, the method including: (a) providing an extract produced by lysing the red blood cells in a whole blood sample from a subject, centrifuging the sample to form a supernatant and a pellet, discarding some or all of the supernatant, and resuspending the pellet to form an extract, optionally washing the pellet (e.g., with TE buffer) prior to resuspending the pellet and optionally repeating the centrifuging, discarding, and washing of step (a); (b) lysing cells in the extract to form a lysate; (c) placing the lysate of step (b) in a detection tube and amplifying nucleic acids therein to form an amplified lysate solution including from 40% (w/w) to 95% (w/w) the target nucleic acid (e.g., from 40 to 60%, from 60 to 80%, or from 85 to 95% (w/w) target nucleic acid) and from 5% (w/w) to 60% (w/w) nontarget nucleic acid (e.g., from 5 to 20%, from 20 to 40%, or from 40 to 60% (w/w) nontarget nucleic acid); (d) following step (c), adding to the detection tube from 1×10⁶ to 1×10¹³ magnetic particles per milliliter of the amplified lysate solution, wherein the magnetic particles have a mean diameter of from 700 nm to 1200 nm and binding moieties on their surface, the binding moieties operative to alter aggregation of the magnetic particles in the presence of the target nucleic acid or a multivalent binding agent; (e) placing the detection tube in a device, the device including a support defining a well for holding the detection tube including the magnetic particles and the target nucleic acid, and having an RF coil disposed about the well, the RF coil configured to detect a signal produced by exposing the liquid sample to a bias magnetic field created using one or more magnets and an RF pulse sequence; (f) exposing the sample to a bias magnetic field and an RF pulse sequence; (g) following step (f), measuring the signal from the detection tube; and (h) on the basis of the result of step (g), detecting the target nucleic acid, wherein step (g) is carried out without any prior purification of the amplified lysate solution. In particular embodiments, step (b) includes combining the extract with beads to form a mixture and agitating the mixture to form a lysate. The magnetic particles can include one or more populations having a first probe and a second probe conjugated to their surface, the first probe operative to bind to a first segment of the target nucleic acid and the second probe operative to bind to a second segment of the target nucleic acid, wherein the magnetic particles form aggregates in the presence of the target nucleic acid. Alternatively, the assay can be a disaggregation assay in which the magnetic particles include a first population having a first binding moiety on their surface and a second population having a second binding moiety on their surface, and the multivalent binding moiety including a first probe and a second probe, the first probe operative to bind to the first binding moiety and the second probe operative to bind to a second binding moiety, the binding moieties and multivalent binding moiety operative to alter an aggregation of the magnetic particles in the presence of the target nucleic acid. In certain embodiments, the magnetic particles are substantially monodisperse; exhibit nonspecific reversibility in the absence of the analyte and multivalent binding agent; and/or the magnetic particles further include a surface decorated with a blocking agent selected from albumin, fish skin gelatin, gamma globulin, lysozyme, casein, peptidase, and an amine-bearing moiety (e.g., amino polyethyleneglycol, glycine, ethylenediamine, or amino dextran). In particular embodiments, the lysate further includes a buffer, from 0.1% to 3% (w/w) albumin (e.g., from 0.1% to 0.5%, 0.3% to 0.7%, 0.5% to 1%, 0.8% to 2%, or from 1.5% to 3% (w/w) albumin), from 0.01% to 0.5% nonionic surfactant (e.g., from 0.01% to 0.05%, 0.05% to 0.1%, 0.05% to 0.2%, 0.1% to 0.3%, 0.2% to 0.4%, or from 0.3% to 0.5% nonionic surfactant), or a combination thereof. In still other embodiments, the magnetic particles include a surface decorated with 40 μg to 100 μg (e.g., 40 μg to 60 μg, 50 μg to 70 μg, 60 μg to 80 μg, or 80 μg to 100 μg,) of one or more proteins per milligram of the magnetic particles. The lysate can include a multivalent binding agent bearing a plurality of analytes conjugated to a polymeric scaffold.

The invention features a method for detecting the presence of a Candida species in a liquid sample, the method including: (a) lysing the Candida cells in the liquid sample; (b) amplifying a nucleic acid to be detected in the presence of a forward primer and a reverse primer, each of which is universal to multiple Candida species to form a solution including a Candida amplicon; (c) contacting the solution with magnetic particles to produce a liquid sample including from 1×10⁶ to 1×10¹³ magnetic particles per milliliter of the liquid sample (e.g., from 1×10⁶ to 1×10⁸, 1×10⁷ to 1×10⁸, 1×10⁷ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or 1×10¹⁰ to 1×10¹³ magnetic particles per milliliter), wherein the magnetic particles have a mean diameter of from 700 nm to 1200 nm (e.g., from 700 to 850, 800 to 950, 900 to 1050, or from 1000 to 1200 nm), a T₂ relaxivity per particle of from 1×10⁹ to 1×10¹² mM⁻¹s⁻¹ (e.g., from 1×10⁸ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or from 1×10¹⁰ to 1×10¹² mM⁻¹s⁻¹), and binding moieties on their surface, the binding moieties operative to alter aggregation of the magnetic particles in the presence of the Candida amplicon or a multivalent binding agent; (d) placing the liquid sample in a device, the device including a support defining a well for holding the liquid sample including the magnetic particles and the Candida amplicon, and having an RF coil disposed about the well, the RF coil configured to detect a signal produced by exposing the liquid sample to a bias magnetic field created using one or more magnets and an RF pulse sequence; (e) exposing the sample to a bias magnetic field and an RF pulse sequence; (f) following step (e), measuring the signal; and (g) on the basis of the result of step (f), determining whether the Candida species was present in the sample. In certain embodiments, the magnetic particles are substantially monodisperse; exhibit nonspecific reversibility in the absence of the analyte and multivalent binding agent; and/or the magnetic particles further include a surface decorated with a blocking agent selected from albumin, fish skin gelatin, gamma globulin, lysozyme, casein, peptidase, and an amine-bearing moiety (e.g., amino polyethyleneglycol, glycine, ethylenediamine, or amino dextran). In particular embodiments, the liquid sample further includes a buffer, from 0.1% to 3% (w/w) albumin (e.g., from 0.1% to 0.5%, 0.3% to 0.7%, 0.5% to 1%, 0.8% to 2%, or from 1.5% to 3% (w/w) albumin), from 0.01% to 0.5% nonionic surfactant (e.g., from 0.01% to 0.05%, 0.05% to 0.1%, 0.05% to 0.2%, 0.1% to 0.3%, 0.2% to 0.4%, or from 0.3% to 0.5% nonionic surfactant), or a combination thereof. In still other embodiments, the magnetic particles include a surface decorated with 40 μg to 100 μg (e.g., 40 μg to 60 μg, 50 μg to 70 μg, 60 μg to 80 μg, or 80 μg to 100 μg,) of one or more proteins per milligram of the magnetic particles. The liquid sample can include a multivalent binding agent bearing a plurality of analytes conjugated to a polymeric scaffold. The forward primer can include, for example, the sequence 5′-GGC ATG CCT GTT TGA GCG TC-3′ (SEQ ID NO. 1). The reverse primer can include, for example, the sequence 5′-GCT TAT TGA TAT GCT TAA GTT CAG CGG GT-3′ (SEQ ID NO. 2). In certain embodiments, (i) the Candida species is Candida albicans, the first probe includes the oligonucleotide sequence 5′-ACC CAG CGG TTT GAG GGA GAA AC-3′ (SEQ ID NO. 3), and the second probe includes the oligonucleotide sequence 5′-AAA GTT TGA AGA TAT ACG TGG TGG ACG TTA-3′ (SEQ ID NO. 4); (ii) the Candida species is Candida krusei and the first probe and the second probe include an oligonucleotide sequence selected from: 5′-CGC ACG CGC AAG ATG GAA ACG-3′ (SEQ ID NO. 5), 5′-AAG TTC AGC GGG TAT TCC TAC CT-3′ (SEQ ID NO. 6), and 5′-AGC TTT TTG TTG TCT CGC AAC ACT CGC-3′ (SEQ ID NO. 32); (iii) the Candida species is Candida glabrata, the first probe includes the oligonucleotide sequence: 5′-CTA CCA AAC ACA ATG TGT TTG AGA AG-3′ (SEQ ID NO. 7), and the second probe includes the oligonucleotide sequence: 5′-CCT GAT TTG AGG TCA AAC TTA AAG ACG TCT G-3′ (SEQ ID NO. 8); and (iv) the Candida species is Candida parapsilosis or Candida tropicalis and the first probe and the second probe include an oligonucleotide sequence selected from: 5′-AGT CCT ACC TGA TTT GAG GTCNitIndAA-3′ (SEQ ID NO. 9), 5′-CCG NitIndGG GTT TGA GGG AGA AAT-3′ (SEQ ID NO. 10), AAA GTT ATG AAATAA ATT GTG GTG GCC ACT AGC (SEQ ID NO. 33), ACC CGG GGGTTT GAG GGA GAA A (SEQ ID NO. 34), AGT CCT ACC TGA TTT GAG GTC GAA (SEQ ID NO. 35), and CCG AGG GTT TGA GGG AGA AAT (SEQ ID NO. 36). In certain embodiments, steps (a) through (h) are completed within 4 hours (e.g., within 3.5 hours, 3.0 hours, 2.5 hours, 2 hours, 1.5 hours, or 1 hour or less). In particular embodiments, the magnetic particles include two populations, a first population bearing the first probe on its surface, and the second population bearing the second probe on its surface. In another embodiment, the magnetic particles are a single population bearing both the first probe and the second probe on the surface of the magnetic particles. The magnetic particles can include one or more populations having a first probe and a second probe conjugated to their surface, the first probe operative to bind to a first segment of the Candida amplicon and the second probe operative to bind to a second segment of the Candida amplicon, wherein the magnetic particles form aggregates in the presence of the target nucleic acid. Alternatively, the assay can be a disaggregation assay in which the magnetic particles include a first population having a first binding moiety on their surface and a second population having a second binding moiety on their surface, and the multivalent binding moiety including a first probe and a second probe, the first probe operative to bind to the first binding moiety and the second probe operative to bind to a second binding moiety, the binding moieties and multivalent binding moiety operative to alter an aggregation of the magnetic particles in the presence of the Candida amplicon. In particular embodiments, the method can produce (i) a coefficient of variation in the T2 value of less than 20% on Candida positive samples; (ii) at least 95% correct detection at less than or equal to 5 cells/mL in samples spiked into 50 individual healthy patient blood samples; (iii) at least 95% correct detection less than or equal to 5 cells/mL in samples spiked into 50 individual unhealthy patient blood samples; and/or (iv) greater than or equal to 80% correct detection in clinically positive patient samples (i.e., Candida positive by another technique, such as by cell culture) starting with 2 mL of blood.

The invention features a method for detecting the presence of a Candida species in a whole blood sample, the method including: (a) providing an extract produced by lysing the red blood cells in a whole blood sample from a subject; (b) centrifuging the sample to form a supernatant and a pellet, discarding some or all of the supernatant; (c) washing the pellet (e.g., with TE buffer) by mixing the pellet with a buffer, agitating the sample (e.g., by vortexing), centrifuging the sample to form a supernatant and a pellet, discarding some or all of the supernatant; (d) optionally repeating steps (b) and (c); (e) bead beating the pellet to form a lysate in the presence of a buffer (e.g., TE buffer); (f) centrifuging the sample to form a supernatant containing the lysate; (g) amplifying nucleic acids in the lysate of step (f) to form a Candida amplicon; and (h) detecting the presence of the Candida amplicon, wherein, the method can produce (i) at least 95% correct detection at less than or equal to 5 cells/mL in samples spiked into 50 individual healthy patient blood samples; (ii) at least 95% correct detection less than or equal to 5 cells/mL in samples spiked into 50 individual unhealthy patient blood samples; and/or (iii) greater than or equal to 80% correct detection in clinically positive patient samples (i.e., Candida positive by cell culture) starting with 2 mL of blood at step(a).

The invention features a method for detecting the presence of a pathogen in a whole blood sample, the method including the steps of: (a) providing from 0.05 to 4.0 mL of the whole blood sample (e.g., from 0.05 to 0.25, 0.25 to 0.5, 0.25 to 0.75, 0.4 to 0.8, 0.5 to 0.75, 0.6 to 0.9, 0.65 to 1.25, 1.25 to 2.5, 2.5 to 3.5, or 3.0 to 4.0 mL of whole blood); (b) placing an aliquot of the sample of step (a) in a container and amplifying a target nucleic acid in the sample to form an amplified solution including the target nucleic acid, wherein the target nucleic acid is characteristic of the pathogen to be detected; (c) placing the amplified liquid sample in a detecting device; (d) on the basis of the result of step (c), detecting the pathogen, wherein the pathogen is selected from bacteria and fungi, and wherein the method is capable of detecting a pathogen concentration of 10 cells/mL (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, or 50 cells/mL) in the whole blood sample. The detecting device can detect the pathogen via an optical, fluorescent, mass, density, magnetic, chromatographic, and/or electrochemical measurement of the amplified liquid sample. In certain embodiments, steps (a) through (d) are completed within 3 hours (e.g., within 3.2, 2.9, 2.7, 2.5, 2.3, 2.2, 2.1, 2.0, 1.9, 1.8, 1.7, 1.6, or 1.5 hours or 1 hour). In still other embodiments, step (c) is carried out without any prior purification of the amplified solution, and/or the liquid sample of step (c) includes whole blood proteins and non-target oligonucleotides. In certain embodiments, the pathogen is selected from bacteria and fungi. The pathogen can be any bacterial or fungal pathogen described herein.

The invention also features a method for detecting the presence of a pathogen in a whole blood sample, the method including the steps of: (a) providing a whole blood sample from a subject; (b) mixing from 0.05 to 4.0 mL of the whole blood sample (e.g., from 0.05 to 0.25, 0.25 to 0.5, 0.25 to 0.75, 0.4 to 0.8, 0.5 to 0.75, 0.6 to 0.9, 0.65 to 1.25, 1.25 to 2.5, 2.5 to 3.5, or 3.0 to 4.0 mL of whole blood) with an erythrocyte lysis agent solution to produce disrupted red blood cells; (c) following step (b), centrifuging the sample to form a supernatant and a pellet, discarding some or all of the supernatant, and resuspending the pellet to form an extract, optionally washing the pellet (e.g., with TE buffer) prior to resuspending the pellet and optionally repeating step (c); (d) lysing cells of the extract to form a lysate; (e) placing the lysate of step (d) in a container and amplifying a target nucleic acid in the lysate to form an amplified lysate solution including the target nucleic acid, wherein the target nucleic acid is characteristic of the pathogen to be detected; (f) following step (e), mixing the amplified lysate solution with from 1×10⁶ to 1×10¹³ magnetic particles per milliliter of the amplified lysate solution to form a liquid sample (e.g., from 1×10⁶ to 1×10⁸, 1×10⁷ to 1×10⁸, 1×10⁷ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or 1×10¹⁰ to 1×10¹³ magnetic particles per milliliter), wherein the magnetic particles have a mean diameter of from 150 nm to 1200 nm (e.g., from 150 to 250, 200 to 350, 250 to 450, 300 to 500, 450 to 650, 500 to 700 nm, 700 to 850, 800 to 950, 900 to 1050, or from 1000 to 1200 nm), a T₂ relaxivity per particle of from 1×10⁸ to 1×10¹² mM⁻¹s⁻¹ (e.g., from 1×10⁸ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or from 1×10¹⁰ to 1×10¹² mM⁻¹s⁻¹), and binding moieties on their surface, the binding moieties operative to alter aggregation of the magnetic particles in the presence of the target nucleic acid or a multivalent binding agent; (g) placing the liquid sample in a device, the device including a support defining a well for holding the detection tube including the magnetic particles and the target nucleic acid, and having an RF coil disposed about the well, the RF coil configured to detect a signal produced by exposing the liquid sample to a bias magnetic field created using one or more magnets and an RF pulse sequence; (h) exposing the sample to a bias magnetic field and an RF pulse sequence; (i) following step (h), measuring the signal from the liquid sample; and (j) on the basis of the result of step (i), detecting the pathogen, wherein the pathogen is selected from bacteria and fungi, and wherein the method is capable of detecting a pathogen concentration of 10 cells/mL (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, or 50 cells/mL) in the whole blood sample. In certain embodiments, steps (a) through (i) are completed within 3 hours (e.g., within 3.2, 2.9, 2.7, 2.5, 2.3, 2.2, 2.1, 2.0, 1.9, 1.8, 1.7, 1.6, 1.5, or for less hours). In still other embodiments, step (i) is carried out without any prior purification of the amplified lysate solution, and/or the liquid sample of step (i) includes whole blood proteins and non-target oligonucleotides. In certain embodiments, the pathogen is selected from bacteria and fungi. The pathogen can be any bacterial or fungal pathogen described herein. In particular embodiments the method is capable of measuring a pathogen concentration of 10 cells/mL in the whole blood sample with a coefficient of variation of less than 15% (e.g., 10 cells/mL with a coefficient of variation of less than 15%, 10%, 7.5%, or 5%; or 25 cells/mL with a coefficient of variation of less than 15%, 10%, 7.5%, or 5%; or 50 cells/mL with a coefficient of variation of less than 15%, 10%, 7.5%, or 5%; or 100 cells/mL with a coefficient of variation of less than 15%, 10%, 7.5%, or 5%). In certain embodiments, the magnetic particles are substantially monodisperse; exhibit nonspecific reversibility in the absence of the analyte and multivalent binding agent; and/or the magnetic particles further include a surface decorated with a blocking agent selected from albumin, fish skin gelatin, gamma globulin, lysozyme, casein, peptidase, and an amine-bearing moiety (e.g., amino polyethyleneglycol, glycine, ethylenediamine, or amino dextran). In particular embodiments, the liquid sample further includes a buffer, from 0.1% to 3% (w/w) albumin (e.g., from 0.1% to 0.5%, 0.3% to 0.7%, 0.5% to 1%, 0.8% to 2%, or from 1.5% to 3% (w/w) albumin), from 0.01% to 0.5% nonionic surfactant (e.g., from 0.01% to 0.05%, 0.05% to 0.1%, 0.05% to 0.2%, 0.1% to 0.3%, 0.2% to 0.4%, or from 0.3% to 0.5% nonionic surfactant), or a combination thereof. In still other embodiments, the magnetic particles include a surface decorated with 40 μg to 100 μg (e.g., 40 μg to 60 μg, 50 μg to 70 μg, 60 μg to 80 μg, or 80 μg to 100 μg,) of one or more proteins per milligram of the magnetic particles. The liquid sample can include a multivalent binding agent bearing a plurality of analytes conjugated to a polymeric scaffold. The method for monitoring can include any of the magnetic assisted agglomeration methods described herein. The magnetic particles can include one or more populations having a first probe and a second probe conjugated to their surface, the first probe operative to bind to a first segment of the target nucleic acid and the second probe operative to bind to a second segment of the target nucleic acid, wherein the magnetic particles form aggregates in the presence of the target nucleic acid. Alternatively, the assay can be a disaggregation assay in which the magnetic particles include a first population having a first binding moiety on their surface and a second population having a second binding moiety on their surface, and the multivalent binding moiety including a first probe and a second probe, the first probe operative to bind to the first binding moiety and the second probe operative to bind to a second binding moiety, the binding moieties and multivalent binding moiety operative to alter an aggregation of the magnetic particles in the presence of the target nucleic acid.

The invention further features a method for detecting the presence of a virus in a whole blood sample, the method including the steps of: (a) providing a plasma sample from a subject; (b) mixing from 0.05 to 4.0 mL of the plasma sample (e.g., from 0.05 to 0.25, 0.25 to 0.5, 0.25 to 0.75, 0.4 to 0.8, 0.5 to 0.75, 0.6 to 0.9, 0.65 to 1.25, 1.25 to 2.5, 2.5 to 3.5, or 3.0 to 4.0 mL of whole blood) with a lysis agent to produce a mixture comprising disrupted viruses; (c) placing the mixture of step (b) in a container and amplifying a target nucleic acid in the filtrate to form an amplified filtrate solution including the target nucleic acid, wherein the target nucleic acid is characteristic of the virus to be detected; (d) following step (c), mixing the amplified filtrate solution with from 1×10⁶ to 1×10¹³ magnetic particles per milliliter of the amplified filtrate solution to form a liquid sample (e.g., from 1×10⁶ to 1×10⁸, 1×10⁷ to 1×10⁸, 1×10⁷ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or 1×10¹⁰ to 1×10¹³ magnetic particles per milliliter), wherein the magnetic particles have a mean diameter of from 150 nm to 1200 nm (e.g., from 150 to 250, 200 to 350, 250 to 450, 300 to 500, 450 to 650, 500 to 700 nm, 700 to 850, 800 to 950, 900 to 1050, or from 1000 to 1200 nm), a T₂ relaxivity per particle of from 1×10⁸ to 1×10¹² mM⁻¹s⁻¹ (e.g., from 1×10⁸ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or from 1×10¹⁰ to 1×10¹² mM⁻¹s⁻¹), and binding moieties on their surface, the binding moieties operative to alter aggregation of the magnetic particles in the presence of the target nucleic acid or a multivalent binding agent; (e) placing the liquid sample in a device, the device including a support defining a well for holding the detection tube including the magnetic particles and the target nucleic acid, and having an RF coil disposed about the well, the RF coil configured to detect a signal produced by exposing the liquid sample to a bias magnetic field created using one or more magnets and an RF pulse sequence; (f) exposing the liquid sample to a bias magnetic field and an RF pulse sequence; (g) following step (f), measuring the signal from the liquid sample; and (h) on the basis of the result of step (g), detecting the virus, wherein the method is capable of detecting fewer than 100 virus copies (e.g., fewer than 80, 70, 60, 50, 40, 30, 20, or 10 copies) in the whole blood sample. In certain embodiments, steps (a) through (g) are completed within 3 hours (e.g., within 3.2, 2.9, 2.7, 2.5, 2.3, 2.2, 2.1, 2.0, 1.9, 1.8, 1.7, 1.6, 1.5 hours, or 1 hour or less). The virus can be any viral pathogen described herein. In certain embodiments, the magnetic particles are substantially monodisperse; exhibit nonspecific reversibility in the absence of the analyte and multivalent binding agent; and/or the magnetic particles further include a surface decorated with a blocking agent selected from albumin, fish skin gelatin, gamma globulin, lysozyme, casein, peptidase, and an amine-bearing moiety (e.g., amino polyethyleneglycol, glycine, ethylenediamine, or amino dextran). In particular embodiments, the liquid sample further includes a buffer, from 0.1% to 3% (w/w) albumin (e.g., from 0.1% to 0.5%, 0.3% to 0.7%, 0.5% to 1%, 0.8% to 2%, or from 1.5% to 3% (w/w) albumin), from 0.01% to 0.5% nonionic surfactant (e.g., from 0.01% to 0.05%, 0.05% to 0.1%, 0.05% to 0.2%, 0.1% to 0.3%, 0.2% to 0.4%, or from 0.3% to 0.5% nonionic surfactant), or a combination thereof. In still other embodiments, the magnetic particles include a surface decorated with 40 μg to 100 μg (e.g., 40 μg to 60 μg, 50 μg to 70 μg, 60 μg to 80 μg, or 80 μg to 100 μg,) of one or more proteins per milligram of the magnetic particles. The liquid sample can include a multivalent binding agent bearing a plurality of analytes conjugated to a polymeric scaffold. The method for monitoring can include any of the magnetic assisted agglomeration methods described herein. The magnetic particles can include one or more populations having a first probe and a second probe conjugated to their surface, the first probe operative to bind to a first segment of the target nucleic acid and the second probe operative to bind to a second segment of the target nucleic acid, wherein the magnetic particles form aggregates in the presence of the target nucleic acid. Alternatively, the assay can be a disaggregation assay in which the magnetic particles include a first population having a first binding moiety on their surface and a second population having a second binding moiety on their surface, and the multivalent binding moiety including a first probe and a second probe, the first probe operative to bind to the first binding moiety and the second probe operative to bind to a second binding moiety, the binding moieties and multivalent binding moiety operative to alter an aggregation of the magnetic particles in the presence of the target nucleic acid.

In any of the systems and methods of the invention in which a PCR amplification is performed, the PCR method can be real time PCR for quantifying the amount of a target nucleic acid present in a sample.

The invention features a method of quantifying a target nucleic acid molecule in a sample by amplifying the target nucleic acid molecule (e.g., using PCR or isothermal amplification) in an amplification reaction mixture in a detection tube resulting in the production of amplicons corresponding to the target nucleic acid molecule, wherein the amplification reaction mixture includes (1) a target nucleic acid molecule, (2) biotin labeled amplification primers specific for the target nucleic acid molecule, and (3) avidin labeled superparamagnetic particles. In this method, the amplification is performed in a device including a support defining a well for holding the detection tube including the superparamagnetic particles and the target nucleic acid molecule, and having an RF coil disposed about the well, the RF coil configured to detect a signal produced by exposing the sample to a bias magnetic field created using one or more magnets and an RF pulse sequence. In this method, the amplification includes the following steps:

-   -   (a) performing one or more cycles of amplification;     -   (b) exposing the amplification reaction mixture to conditions         permitting the aggregation or disaggregation of the avidin         labeled superparamagnetic particles,     -   (c) exposing the sample to a bias magnetic field and an RF pulse         sequence;     -   (d) following step (c), measuring the signal from the detection         tube;     -   (e) repeating steps (a)-(d) until a desired amount of         amplification is obtained; and     -   (f) on the basis of the result of step (d), quantifying the         amplicons present at the corresponding cycle of amplification.

In this method, the initial quantity of target nucleic acid molecule in the sample is determined based on the quantity of amplicons determined at each cycle of the PCR.

The invention further features a method of quantifying a target nucleic acid molecule in a sample by amplifying the target nucleic acid molecule (e.g., using PCR or isothermal amplification) in an amplification reaction mixture in a detection tube resulting in the production of amplicons corresponding to the target nucleic acid molecule. In this method, the amplification reaction mixture includes (1) a target nucleic acid molecule, (2) amplification primers including a 5′ overhang, wherein the amplification primers are specific for the target nucleic acid molecule, and (3) oligonucleotide labeled superparamagnetic particles, wherein the oligonucleotide label is substantially complementary to the 5′ overhang of the amplification primers. In this method, the amplification is performed in a device including a support defining a well for holding the detection tube including the superparamagnetic particles and the target nucleic acid molecule, and having an RF coil disposed about the well, the RF coil configured to detect a signal produced by exposing the sample to a bias magnetic field created using one or more magnets and an RF pulse sequence. In this method, the amplification includes the following steps:

-   -   (a) performing one or more cycles of amplification;     -   (b) exposing the amplification reaction mixture to conditions         permitting the hybridization of the oligonucleotide labeled         superparamagnetic particles with the 5′ overhang;     -   (c) exposing the sample to a bias magnetic field and an RF pulse         sequence;     -   (d) following step (c), measuring the signal from the detection         tube;     -   (e) repeating steps (a)-(d) until a desired amount of         amplification is obtained; and     -   (f) on the basis of the result of step (d), quantifying the         amplicons present at the corresponding cycle of amplification.

In this method, the initial quantity of target nucleic acid molecule in the sample is determined based on the quantity of amplicons determined at each cycle of the amplification.

The invention further features a method of quantifying a target nucleic acid molecule in a sample by amplifying the target nucleic acid molecule (e.g., using PCR or isothermal amplification) in an amplification reaction mixture in a detection tube resulting in the production of amplicons corresponding to the target nucleic acid molecule. In this method the amplification reaction mixture includes (1) a target nucleic acid molecule, (2) amplification primers specific for the target nucleic acid molecule, and (3) oligonucleotide labeled superparamagnetic particles, wherein the oligonucleotide label contains a hairpin structure and a portion of the hairpin structure is substantially complementary to a portion of the nucleic acid sequence of the amplicons. In this method, the amplification is performed in a device including a support defining a well for holding the detection tube including the superparamagnetic particles and the target nucleic acid molecule, and having an RF coil disposed about the well, the RF coil configured to detect a signal produced by exposing the sample to a bias magnetic field created using one or more magnets and an RF pulse sequence. This amplification of this method includes the following steps:

-   -   (a) performing one or more cycles of amplification;     -   (b) exposing the amplification reaction mixture to conditions         permitting the hybridization of the portion of the hairpin         structure of (3) with the amplicons;     -   (c) exposing the sample to a bias magnetic field and an RF pulse         sequence;     -   (d) following step (c), measuring the signal from the detection         tube;     -   (e) repeating steps (a)-(d) until a desired amount of         amplification is obtained; and     -   (f) on the basis of the result of step (d), quantifying the         amplicons present at the corresponding cycle of amplification.

In this method, the initial quantity of target nucleic acid molecule in the sample is determined based on the quantity of amplicons determined at each cycle of the amplification.

The invention also features a method of quantifying a target nucleic acid molecule in a sample by amplifying the target nucleic acid molecule using PCR in an amplification reaction mixture in a detection tube resulting in the production of amplicons corresponding to the target nucleic acid molecule. In this method, the amplification reaction mixture includes (1) a target nucleic acid molecule, (2) a polymerase with 5′exonuclease activity, (3) amplification primers specific for the target nucleic acid molecule, and (4) oligonucleotide tethered superparamagnetic particles, wherein the oligonucleotide tether connects at least two superparamagnetic particles and the oligonucleotide tether is substantially complementary to a portion of the nucleic acid sequence of the amplicons. In this method, the amplification is performed in a device including a support defining a well for holding the detection tube including the superparamagnetic particles and the target nucleic acid molecule, and having an RF coil disposed about the well, the RF coil configured to detect a signal produced by exposing the sample to a bias magnetic field created using one or more magnets and an RF pulse sequence. The amplification of this method includes the following steps:

-   -   (a) performing one or more cycles of PCR under conditions         permitting the hybridization of the oligonucleotide tether to an         amplicon during the extension phase of the PCR, wherein during         the extension phase of the PCR, the 5′ exonuclease activity of         the polymerase untethers the at least two superparamagnetic         particles permitting a decrease in superparamagnetic particle         aggregation;     -   (b) exposing the sample to a bias magnetic field and an RF pulse         sequence;     -   (c) following step (b), measuring the signal from the detection         tube;     -   (d) repeating steps (a)-(c) until the PCR is complete; and     -   (e) on the basis of the result of step (c), quantifying the         amplicons present at the corresponding cycle of PCR.

In this method, the initial quantity of target nucleic acid molecule in the sample is determined based on the quantity of amplicons determined at each cycle of the PCR.

The invention also features a method of quantifying a target nucleic acid molecule in a sample by amplifying the target nucleic acid molecule (e.g., using PCR or isothermal amplification) in an amplification reaction mixture in a detection tube resulting in the production of amplicons corresponding to the target nucleic acid molecule. In this method, the amplification reaction mixture includes (1) a target nucleic acid molecule, (2) amplification primers specific for the target nucleic acid molecule, and (3) superparamagnetic particles labeled with a plurality of oligonucleotides, wherein a first group of the plurality of oligonucleotides are substantially complementary to a portion of the nucleic acid sequence of the amplicons and substantially complementary to a second group of the plurality of oligonucleotides, wherein the first group of the plurality of oligonucleotides has a lesser hybridization affinity for the second group of the plurality of oligonucleotides than for the amplicons. In this method, the amplification is performed in a device including a support defining a well for holding the detection tube including the superparamagnetic particles and the target nucleic acid molecule, and having an RF coil disposed about the well, the RF coil configured to detect a signal produced by exposing the sample to a bias magnetic field created using one or more magnets and an RF pulse sequence. The amplification of this method includes the following steps:

-   -   (a) performing one or more cycles of amplification;     -   (b) exposing the amplification reaction mixture to conditions         permitting the preferential hybridization of the first group of         the plurality of oligonucleotides with the amplicons thereby         permitting disaggregation of the superparamagnetic particles;     -   (c) exposing the sample to a bias magnetic field and an RF pulse         sequence;     -   (d) following step (c), measuring the signal from the detection         tube;     -   (e) repeating steps (a)-(d) until a desired amount of         amplification is obtained; and     -   (f) on the basis of the result of step (d); quantifying the         amplicons present at the corresponding cycle of amplification.

In this method, the initial quantity of target nucleic acid molecule in the sample is determined based on the quantity of amplicons determined at each cycle of the amplification.

The invention further features a method of quantifying a target nucleic acid molecule in a sample by amplifying the target nucleic acid molecule (e.g., using PCR or isothermal amplification) in an amplification reaction mixture in a detection tube resulting in the production of amplicons corresponding to the target nucleic acid molecule. In this method, the amplification reaction mixture includes (1) a target nucleic acid molecule, (2) amplification primers specific for the target nucleic acid molecule, and (3) superparamagnetic particles. In this method, the amplification is performed in a device including a support defining a well for holding the detection tube including the superparamagnetic particles and the target nucleic acid molecule, and having an RF coil disposed about the well, the RF coil configured to detect a signal produced by exposing the sample to a bias magnetic field created using one or more magnets and an RF pulse sequence. The amplification of this method including the following steps:

-   -   (a) performing one or more cycles of amplification;     -   (b) exposing the amplification reaction mixture to conditions         permitting the aggregation or disaggregation of the         superparamagnetic particles,     -   (c) exposing the sample to a bias magnetic field and an RF pulse         sequence;     -   (d) following step (c), measuring the signal from the detection         tube;     -   (e) repeating steps (a)-(d) until a desired amount of         amplification is obtained; and     -   (f) on the basis of the result of step (d), quantifying the         amplicons present at the corresponding cycle of amplification.

In this method, the initial quantity of target nucleic acid molecule in the sample is determined based on the quantity of amplicons determined at each cycle of the amplification.

In any of the foregoing methods of quantifying a target nucleic acid molecule, the detection tube can remained sealed throughout the amplification reaction. The superparamagnetic particles of these methods can be greater or less than 100 nm in diameter (e.g., 30 nm in diameter).

Also, in any of the foregoing methods of quantifying a target nucleic acid molecule, the methods can further include applying a magnetic field to the detection tube following the measuring the signal from the detection tube, resulting in the sequestration of the superparamagnetic particles to the side of the detection tube, and releasing the magnetic field subsequent to the completion of one or more additional cycles of amplification.

Also, in any of the foregoing methods of quantifying a target nucleic acid molecule, the sample can, e.g., not include isolated nucleic acid molecules prior to step (a) (e.g., the sample can be whole blood or not contain a target nucleic acid molecule prior to step (a)).

The invention features a method of monitoring one or more analytes in a liquid sample derived from a patient for the diagnosis, management, or treatment of a medical condition in a patient, the method including (a) combining with the liquid sample from 1×10⁶ to 1×10¹³ magnetic particles per milliliter of the liquid sample (e.g., from 1×10⁶ to 1×10⁸, 1×10⁷ to 1×10⁸, 1×10⁷ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or 1×10¹⁰ to 1×10¹³ magnetic particles per milliliter), wherein the magnetic particles have a mean diameter of from 150 nm to 1200 nm (e.g., from 150 to 250, 200 to 350, 250 to 450, 300 to 500, 450 to 650, 500 to 700 nm, 700 to 850, 800 to 950, 900 to 1050, or from 1000 to 1200 nm), and a T₂ relaxivity per particle of from 1×10⁸ to 1×10¹² mM⁻¹s⁻¹ (e.g., from 1×10⁸ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or from 1×10¹⁰ to 1×10¹² mM⁻¹s⁻¹), and wherein the magnetic particles have binding moieties on their surfaces, the binding moieties operative to alter the specific aggregation of the magnetic particles in the presence of the one or more analytes or a multivalent binding agent; (b) placing the liquid sample in a device, the device including a support defining a well for holding the liquid sample including the magnetic particles and the one or more analytes, and having an RF coil disposed about the well, the RF coil configured to detect a signal produced by exposing the liquid sample to a bias magnetic field created using one or more magnets and an RF pulse sequence; (c) exposing the sample to the bias magnetic field and the RF pulse sequence; (d) following step (c), measuring the signal; (e) on the basis of the result of step (d), monitoring the one or more analytes; and (f) using the result of step (e) to diagnose, manage, or treat the medical condition. In one embodiment, the one or more analytes include creatinine. In another embodiment, the patient is immunocompromised, and the one or more analytes include an analyte selected from pathogen-associated analytes, antibiotic agents, antifungal agents, and antiviral agents (e.g., the one or more analytes can include Candida spp., tacrolimus, fluconazole, and/or creatinine). In still another embodiment, the patient has cancer, and the one or more analytes are selected from anticancer agents, and genetic markers present in a cancer cell. The patient can have, or be at risk of, an infection, and the one or more analytes include an analyte selected from pathogen-associated analytes, antibiotic agents, antifungal agents, and antiviral agents. The patient can have an immunoinflammatory condition, and the one or more analytes include an analyte selected from antiinflammatory agents and TNF-alpha. The patient can have heart disease, and the one or more analytes can include a cardiac marker. The patient can have HIV/AIDS, and the one or more analytes can include CD3, viral load, and AZT. In certain embodiments, the method is used to monitor the liver function of the patient, and wherein the one or more analytes are selected from albumin, aspartate transaminase, alanine transaminase, alkaline phosphatase, gamma glutamyl transpeptidase, bilirubin, alpha fetoprotein, lactase dehydrogenase, mitochondrial antibodies, and cytochrome P450. For example, the one or more analytes include cytochrome P450 polymorphisms, and the ability of the patient to metabolize a drug is evaluated. The method can include identifying the patient as a poor metabolizer, a normal metabolizer, an intermediate metabolizer, or an ultra rapid metabolizer. The method can be used to determine an appropriate dose of a therapeutic agent in a patient by (i) administering the therapeutic agent to the patient; (ii) following step (i), obtaining a sample including the therapeutic agent or metabolite thereof from the patient; (iii) contacting the sample with the magnetic particles and exposing the sample to the bias magnetic field and the RF pulse sequence and detecting a signal produced by the sample; and (iv) on the basis of the result of step (iii), determining the concentration of the therapeutic agent or metabolite thereof. The therapeutic agent can be an anticancer agent, antibiotic agent, antifungal agent, or any therapeutic agent described herein. In any of the above methods of monitoring, the monitoring can be intermittent (e.g., periodic), or continuous. In certain embodiments, the magnetic particles are substantially monodisperse; exhibit nonspecific reversibility in the absence of the analyte and multivalent binding agent; and/or the magnetic particles further include a surface decorated with a blocking agent selected from albumin, fish skin gelatin, gamma globulin, lysozyme, casein, peptidase, and an amine-bearing moiety (e.g., amino polyethyleneglycol, glycine, ethylenediamine, or amino dextran). In particular embodiments, the liquid sample further includes a buffer, from 0.1% to 3% (w/w) albumin (e.g., from 0.1% to 0.5%, 0.3% to 0.7%, 0.5% to 1%, 0.8% to 2%, or from 1.5% to 3% (w/w) albumin), from 0.01% to 0.5% nonionic surfactant (e.g., from 0.01% to 0.05%, 0.05% to 0.1%, 0.05% to 0.2%, 0.1% to 0.3%, 0.2% to 0.4%, or from 0.3% to 0.5% nonionic surfactant), or a combination thereof. In still other embodiments, the magnetic particles include a surface decorated with 40 μg to 100 μg (e.g., 40 μg to 60 μg, 50 μg to 70 μg, 60 μg to 80 μg, or 80 μg to 100 μg,) of one or more proteins per milligram of the magnetic particles. The liquid sample can include a multivalent binding agent bearing a plurality of analytes conjugated to a polymeric scaffold. The method for monitoring can include any of the magnetic assisted agglomeration methods described herein.

The invention features a method of diagnosing sepsis in a subject, the method including (a) obtaining a liquid sample derived from the blood of a patient; (b) preparing a first assay sample by combining with a portion of the liquid sample from 1×10⁶ to 1×10¹³ magnetic particles per milliliter of the liquid sample (e.g., from 1×10⁶ to 1×10⁸, 1×10⁷ to 1×10⁸, 1×10⁷ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or 1×10¹⁰ to 1×10¹³ magnetic particles per milliliter), wherein the magnetic particles have a mean diameter of from 150 nm to 1200 nm (e.g., from 150 to 250, 200 to 350, 250 to 450, 300 to 500, 450 to 650, 500 to 700 nm, 700 to 850, 800 to 950, 900 to 1050, or from 1000 to 1200 nm), and a T₂ relaxivity per particle of from 1×10⁸ to 1×10¹² mM⁻¹s⁻¹ (e.g., from 1×10⁸ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or from 1×10¹⁰ to 1×10¹² mM⁻¹s⁻¹), and wherein the magnetic particles have binding moieties on their surfaces, the binding moieties operative to alter the specific aggregation of the magnetic particles in the presence of one or more pathogen-associated analytes or a multivalent binding agent; (c) preparing a second assay sample by combining with a portion of the liquid sample from 1×10⁶ to 1×10¹³ magnetic particles per milliliter of the liquid sample (e.g., from 1×10⁶ to 1×10⁸, 1×10⁷ to 1×10⁸, 1×10⁷ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or 1×10¹⁰ to 1×10¹³ magnetic particles per milliliter), wherein the magnetic particles have a mean diameter of from 150 nm to 1200 nm (e.g., from 150 to 250, 200 to 350, 250 to 450, 300 to 500, 450 to 650, 500 to 700 nm, 700 to 850, 800 to 950, 900 to 1050, or from 1000 to 1200 nm), and a T₂ relaxivity per particle of from 1×10⁸ to 1×10¹² mM⁻¹s⁻¹ (e.g., from 1×10⁸ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or from 1×10¹⁰ to 1×10¹² mM⁻¹s⁻¹), and wherein the magnetic particles have binding moieties on their surfaces, the binding moieties operative to alter the specific aggregation of the magnetic particles in the presence of one or more analytes characteristic of sepsis selected from GRO-alpha, High mobility group-box 1 protein (HMGB-1), IL-1 receptor, IL-1 receptor antagonist, IL-1b, IL-2, IL-4, IL-6, IL-8, IL-10, IL-12, IL-13, IL-18, macrophage inflammatory protein (MIP-1), macrophage migration inhibitory factor (MIF), osteopontin, RANTES (regulated on activation, normal T-cell expressed and secreted; or CCL5), TNF-α, C-reactive protein (CRP), CD64, monocyte chemotactic protein 1 (MCP-1), adenosine deaminase binding protein (ABP-26), inducible nitric oxide synthetase (iNOS), lipopolysaccharide binding protein, and procalcitonin; (d) placing each assay sample in a device, the device including a support defining a well for holding the liquid sample including the magnetic particles and the one or more analytes, and having an RF coil disposed about the well, the RF coil configured to detect a signal produced by exposing the liquid sample to a bias magnetic field created using one or more magnets and an RF pulse sequence; (e) exposing each assay sample to the bias magnetic field and the RF pulse sequence; (f) following step (e), measuring the signal produced by the first assay sample and the signal produced by the second assay sample; (g) on the basis of the result of step (f), monitoring the one or more analytes of the first assay sample and monitoring the one or more analytes of the second assay sample; and (h) using the results of step (g) to diagnose the subject. In one embodiment, the one or more pathogen-associated analytes of the first assay sample are derived from a pathogen associated with sepsis selected from Acinetobacter baumannii, Aspergillus fumigatis, Bacteroides fragilis, B. fragilis, blaSHV, Burkholderia cepacia, Campylobacter jejuni/coli, Candida guilliermondii, C. albicans, C. glabrata, C. krusei, C. lusitaniae, C. parapsilosis, C. tropicalis, Clostridium pefringens, Coagulase negative Staph, Enterobacter aeraogenes, E. cloacae, Enterobacteriaceae, Enterococcus faecalis, E. faecium, Escherichia coli, Haemophilus influenzae, Kingella Kingae, Klebsiella oxytoca, K. pneumoniae, Listeria monocytogenes, Mec A gene (MRSA), Morganella morgana, Neisseria meningitidis, Neisseria spp. non-meningitidis, Prevotella buccae, P. intermedia, P. melaminogenica, Propionibacterium acnes, Proteus mirabilis, P. vulgaris, Pseudomonas aeruginosa, Salmonella enterica, Serratia marcescens, Staphylococcus aureus, S. haemolyticus, S. maltophilia, S. saprophyticus, Stenotrophomonas maltophilia, S. maltophilia, Streptococcus agalactie, S. bovis, S. dysgalactie, S. mitis, S. mutans, S. pneumoniae, S. pyogenes, and S. sanguinis. The one or more pathogen-associated analytes can be derived from treatment resistant strains of bacteria, such as penicillin-resistant, methicillin-resistant, quinolone-resistant, macrolide-resistant, and/or vancomycin-resistant bacterial strains (e.g., methicillin resistant Staphylococcus aureus or vancomycin-resistant enterococci). In certain embodiments, the one or more analytes of the second assay sample are selected from GRO-alpha, High mobility group-box 1 protein (HMGB-1), IL-1 receptor, IL-1 receptor antagonist, IL-1b, IL-2, IL-4, IL-6, IL-8, IL-10, IL-12, IL-13, IL-18, macrophage inflammatory protein (MIP-1), macrophage migration inhibitory factor (MIF), osteopontin, RANTES (regulated on activation, normal T-cell expressed and secreted; or CCL5), TNF-α, C-reactive protein (CRP), CD64, and monocyte chemotactic protein 1 (MCP-1). In a particular embodiment, the method further includes preparing a third assay sample to monitor the concentration of an antiviral agent, antibiotic agent, or antifungal agent circulating in the blood stream of the subject. In certain embodiments, the subject can be an immunocompromised subject, or a subject at risk of becoming immunocompromised. In any of the above methods of monitoring, the monitoring can be intermittent (e.g., periodic), or continuous. In certain embodiments, the magnetic particles are substantially monodisperse; exhibit nonspecific reversibility in the absence of the analyte and multivalent binding agent; and/or the magnetic particles further include a surface decorated with a blocking agent selected from albumin, fish skin gelatin, gamma globulin, lysozyme, casein, peptidase, and an amine-bearing moiety (e.g., amino polyethyleneglycol, glycine, ethylenediamine, or amino dextran). In particular embodiments, the liquid sample further includes a buffer, from 0.1% to 3% (w/w) albumin (e.g., from 0.1% to 0.5%, 0.3% to 0.7%, 0.5% to 1%, 0.8% to 2%, or from 1.5% to 3% (w/w) albumin), from 0.01% to 0.5% nonionic surfactant (e.g., from 0.01% to 0.05%, 0.05% to 0.1%, 0.05% to 0.2%, 0.1% to 0.3%, 0.2% to 0.4%, or from 0.3% to 0.5% nonionic surfactant), or a combination thereof. In still other embodiments, the magnetic particles include a surface decorated with 40 μg to 100 μg (e.g., 40 μg to 60 μg, 50 μg to 70 μg, 60 μg to 80 μg, or 80 μg to 100 μg,) of one or more proteins per milligram of the magnetic particles. The liquid sample can include a multivalent binding agent bearing a plurality of analytes conjugated to a polymeric scaffold. The method for monitoring can include any of the magnetic assisted agglomeration methods described herein.

The invention further features a method of monitoring one or more analytes in a liquid sample derived from a patient for the diagnosis, management, or treatment of sepsis or SIRS in a patient, the method including: (a) combining with the liquid sample from 1×10⁶ to 1×10¹³ magnetic particles per milliliter of the liquid sample (e.g., from 1×10⁶ to 1×10⁸, 1×10⁷ to 1×10⁸, 1×10⁷ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or 1×10¹⁰ to 1×10¹³ magnetic particles per milliliter), wherein the magnetic particles have a mean diameter of from 150 nm to 1200 nm (e.g., from 150 to 250, 200 to 350, 250 to 450, 300 to 500, 450 to 650, 500 to 700 nm, 700 to 850, 800 to 950, 900 to 1050, or from 1000 to 1200 nm), and a T₂ relaxivity per particle of from 1×10⁸ to 1×10¹² mM⁻¹s⁻¹ (e.g., from 1×10⁸ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or from 1×10¹⁰ to 1×10¹² mM⁻¹s⁻¹), and wherein the magnetic particles have binding moieties on their surfaces, the binding moieties operative to alter the specific aggregation of the magnetic particles in the presence of the one or more analytes or a multivalent binding agent; (b) placing the liquid sample in a device, the device including a support defining a well for holding the liquid sample including the magnetic particles and the one or more analytes, and having an RF coil disposed about the well, the RF coil configured to detect a signal produced by exposing the liquid sample to a bias magnetic field created using one or more magnets and an RF pulse sequence; (c) exposing the sample to the bias magnetic field and the RF pulse sequence; (d) following step (c), measuring the signal; (e) on the basis of the result of step (d), monitoring the one or more analytes; and (f) using the result of step (e) to diagnose, manage, or treat the sepsis or SIRS. The method can include (i) monitoring a pathogen-associated analyte, and (ii) monitoring a second analyte characteristic of sepsis selected from GRO-alpha, High mobility group-box 1 protein (HMGB-1), IL-1 receptor, IL-1 receptor antagonist, IL-1b, IL-2, IL-4, IL-6, IL-8, IL-10, IL-12, IL-13, IL-18, macrophage inflammatory protein (MIP-1), macrophage migration inhibitory factor (MIF), osteopontin, RANTES (regulated on activation, normal T-cell expressed and secreted; or CCL5), TNF-α, C-reactive protein (CRP), CD64, monocyte chemotactic protein 1 (MCP-1), adenosine deaminase binding protein (ABP-26), inducible nitric oxide synthetase (iNOS), lipopolysaccharide binding protein, and procalcitonin. In certain embodiments, the pathogen-associated analyte is derived from a pathogen associated with sepsis selected from Acinetobacter baumannii, Aspergillus fumigatis, Bacteroides fragilis, B. fragilis, blaSHV, Burkholderia cepacia, Campylobacter jejuni/coli, Candida guilliermondii, C. albicans, C. glabrata, C. krusei, C. Lusitaniae, C. parapsilosis, C. tropicalis, Clostridium pefringens, Coagulase negative Staph, Enterobacter aeraogenes, E. cloacae, Enterobacteriaceae, Enterococcus faecalis, E. faecium, Escherichia coli, Haemophilus influenzae, Kingella Kingae, Klebsiella oxytoca, K. pneumoniae, Listeria monocytogenes, Mec A gene (MRSA), Morganella morgana, Neisseria meningitidis, Neisseria spp. non-meningitidis, Prevotella buccae, P. intermedia, P. melaminogenica, Propionibacterium acnes, Proteus mirabilis, P. vulgaris, Pseudomonas aeruginosa, Salmonella enterica, Serratia marcescens, Staphylococcus aureus, S. haemolyticus, S. maltophilia, S. saprophyticus, Stenotrophomonas maltophilia, S. maltophilia, Streptococcus agalactie, S. bovis, S. dysgalactie, S. mitis, S. mutans, S. pneumoniae, S. pyogenes, and S. sanguinis. The pathogen-associated analyte can be derived from a treatment resistant strain of bacteria, such as penicillin-resistant, methicillin-resistant, quinolone-resistant, macrolide-resistant, and/or vancomycin-resistant bacterial strains (e.g., methicillin resistant Staphylococcus aureus or vancomycin-resistant enterococci). In particular embodiments, the second analytes is selected from GRO-alpha, High mobility group-box 1 protein (HMGB-1), IL-1 receptor, IL-1 receptor antagonist, IL-1b, IL-2, IL-4, IL-6, IL-8, IL-10, IL-12, IL-13, IL-18, macrophage inflammatory protein (MIP-1), macrophage migration inhibitory factor (MIF), osteopontin, RANTES (regulated on activation, normal T-cell expressed and secreted; or CCL5), TNF-α, C-reactive protein (CRP), CD64, and monocyte chemotactic protein 1 (MCP-1). In a particular embodiment, the method further includes preparing a third assay sample to monitor the concentration of an antiviral agent, antibiotic agent, or antifungal agent circulating in the blood stream of the subject. In certain embodiments, the subject can be an immunocompromised subject, or a subject at risk of becoming immunocompromised. In any of the above methods of monitoring, the monitoring can be intermittent (e.g., periodic), or continuous. In certain embodiments, the magnetic particles are substantially monodisperse; exhibit nonspecific reversibility in the absence of the analyte and multivalent binding agent; and/or the magnetic particles further include a surface decorated with a blocking agent selected from albumin, fish skin gelatin, gamma globulin, lysozyme, casein, peptidase, and an amine-bearing moiety (e.g., amino polyethyleneglycol, glycine, ethylenediamine, or amino dextran). In particular embodiments, the liquid sample further includes a buffer, from 0.1% to 3% (w/w) albumin (e.g., from 0.1% to 0.5%, 0.3% to 0.7%, 0.5% to 1%, 0.8% to 2%, or from 1.5% to 3% (w/w) albumin), from 0.01% to 0.5% nonionic surfactant (e.g., from 0.01% to 0.05%, 0.05% to 0.1%, 0.05% to 0.2%, 0.1% to 0.3%, 0.2% to 0.4%, or from 0.3% to 0.5% nonionic surfactant), or a combination thereof. In still other embodiments, the magnetic particles include a surface decorated with 40 μg to 100 μg (e.g., 40 μg to 60 μg, 50 μg to 70 μg, 60 μg to 80 μg, or 80 μg to 100 μg,) of one or more proteins per milligram of the magnetic particles. The liquid sample can include a multivalent binding agent bearing a plurality of analytes conjugated to a polymeric scaffold. The method for monitoring can include any of the magnetic assisted agglomeration methods described herein.

In a related aspect, the invention features a method for assisting the specific agglomeration of magnetic particles in a liquid sample, the method including: (i) providing a liquid sample including one or more analytes and the magnetic particles, wherein the magnetic particles have binding moieties on their surfaces, the binding moieties operative to alter the specific aggregation of the magnetic particles in the presence of the one or more analytes or a multivalent binding agent; (ii) exposing the liquid sample to a magnetic field; (iii) removing the liquid sample from the magnetic field; and (iv) repeating step (ii).

The invention further features a method for assisting the specific agglomeration of magnetic particles in a liquid sample by (i) providing a liquid sample including one or more analytes and the magnetic particles, wherein the magnetic particles have binding moieties on their surfaces, the binding moieties operative to alter the specific aggregation of the magnetic particles in the presence of the one or more analytes or a multivalent binding agent; (ii) applying a magnetic field gradient to the liquid sample for a time sufficient to cause concentration of the magnetic particles in a first portion of the liquid sample, the magnetic field gradient being aligned in a first direction relative to the liquid sample; (iii) following step (ii), applying a magnetic field to the liquid sample for a time sufficient to cause concentration of the magnetic particles in a second portion of the liquid sample, the magnetic field being aligned in a second direction relative to the liquid sample; and (iv) optionally repeating steps (ii) and (iii). In certain embodiments, the angle between the first direction and the second direction relative to the liquid sample is between 0° and 180° (e.g., from 0° to 10°, 5° to 120°, 20° to 60°, 30° to 80°, 45° to 90°, 60° to 120°, 80° to 135°, or from 120° to 180°).

The invention features a method for assisting the specific agglomeration of magnetic particles in a liquid sample by (i) providing a liquid sample including one or more analytes and the magnetic particles, wherein the magnetic particles have binding moieties on their surfaces, the binding moieties operative to alter the specific aggregation of the magnetic particles in the presence of the one or more analytes or a multivalent binding agent; (ii) applying a magnetic field gradient to the liquid sample for a time sufficient to cause concentration of the magnetic particles in a first portion of the liquid sample; (iii) following step (ii), agitating the liquid sample; and (iv) repeating step (ii). In certain embodiments, step (iii) includes vortexing the liquid sample, or mixing the sample using any method described herein.

The invention also features a method for assisting the specific agglomeration of magnetic particles in a liquid sample by (i) providing a liquid sample including one or more analytes and the magnetic particles, wherein the magnetic particles have binding moieties on their surfaces, the binding moieties operative to alter the specific aggregation of the magnetic particles in the presence of the one or more analytes or a multivalent binding agent; and (ii) exposing the liquid sample to a gradient magnetic field and rotating the gradient magnetic field about the sample, or rotating the sample within the gradient magnetic field. The sample can be rotated slowly. In certain embodiments, the sample is rotated at a rate of 0.0333 Hz, or less (e.g., from 0.000833 Hz to 0.0333 Hz, from 0.00166 Hz to 0.0333 Hz, or from 0.00333 Hz to 0.0333 Hz). In other embodiments, the method further includes (iii) following step (ii), agitating the liquid sample; and (iv) repeating step (ii).

In any of the above methods for assisting specific agglomeration step (ii) can be repeated from 1 to 100 times (e.g., repeated 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 times, from 10 to 20 times, or from 80 to 100 times). In particular embodiments, the one or more magnets providing the magnetic field gradient within the liquid sample have a maximum field strength of from 0.01 T to 10 T (e.g., from 0.01 T to 0.05 T, 0.05 T to 0.1 T, 0.1 T to 0.5 T, 0.5 T to 1 T, 1 T to 3 T, or from 3 T to 10 T) and wherein the gradient magnetic field varies from 0.1 mT/mm to 10 T/mm across the liquid sample (e.g., from 0.1 mT/mm to 0.5 mT/mm, 0.3 mT/mm to 1 mT/mm, 0.5 mT/mm to 5 mT/mm, 5 mT/mm to 20 mT/mm, 10 mT/mm to 100 mT/mm, 100 mT/mm to 500 mT/mm, 500 mT/mm to 1 T/mm, or from 1 T/mm to 10 T/mm). In certain embodiments of any of the above methods for assisting specific agglomeration, step (ii) includes applying the magnetic field gradient to the liquid sample for a period of from 1 second to 5 minutes (e.g., from 1 to 20 seconds, from 20 to 60 seconds, from 30 seconds to 2 minutes, from 1 minutes to 3 minutes, or from 2 minutes to 5 minutes). In particular embodiments, (i) the liquid sample includes from 1×10⁵ to 1×10¹⁵ of the one or more analytes per milliliter of the liquid sample (e.g., from 1×10⁵ to 1×10⁶, 1×10⁶ to 1×10⁸, 1×10⁷ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹², or 1×10¹¹ to 1×10¹⁵ analytes per milliliter); (ii) the liquid sample includes from 1×10⁶ to 1×10¹³ of the magnetic particles per milliliter of the liquid sample (e.g., from 1×10⁶ to 1×10⁸, 1×10⁷ to 1×10⁸, 1×10⁷ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or 1×10¹⁰ to 1×10¹³ magnetic particles per milliliter); (iii) the magnetic particles have a T₂ relaxivity per particle of from 1×10⁴ to 1×10¹² mM⁻¹s⁻¹ (e.g., from 1×10⁴ to 1×10⁷, 1×10⁶ to 1×10¹⁰, 1×10⁷ to 1×10⁹, 1×10⁸ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or from 1×10¹⁰ to 1×10¹² mM⁻¹s⁻¹); (iv) the magnetic particles have an average diameter of from 150 nm to 1200 nm (e.g., from 150 to 250, 200 to 350, 250 to 450, 300 to 500, 450 to 650, 500 to 700 nm, 700 to 850, 800 to 950, 900 to 1050, or from 1000 to 1200 nm); (v) the magnetic particles are substantially monodisperse; (vi) the magnetic particles in the liquid sample exhibit nonspecific reversibility in the absence of the one or more analytes and multivalent binding agent; (vii) the magnetic particles further include a surface decorated with a blocking agent selected from albumin, fish skin gelatin, gamma globulin, lysozyme, casein, peptidase, and an amine-bearing moiety (e.g., amino polyethyleneglycol, glycine, ethylenediamine, or amino dextran); (viii) the liquid sample further includes a buffer, from 0.1% to 3% (w/w) albumin (e.g., from 0.1% to 0.5%, 0.3% to 0.7%, 0.5% to 1%, 0.8% to 2%, or from 1.5% to 3% (w/w) albumin), from 0.01% to 0.5% nonionic surfactant (e.g., from 0.01% to 0.05%, 0.05% to 0.1%, 0.05% to 0.2%, 0.1% to 0.3%, 0.2% to 0.4%, or from 0.3% to 0.5% nonionic surfactant), or a combination thereof; and/or (ix) the magnetic particles include a surface decorated with 40 μg to 100 μg (e.g., 40 μg to 60 μg, 50 μg to 70 μg, 60 μg to 80 μg, or 80 μg to 100 μg,) of one or more proteins per milligram of the magnetic particles.

The invention features a system for the detection of one or more analytes, the system including: (a) a first unit including (a1) a permanent magnet defining a magnetic field; (a2) a support defining a well for holding a liquid sample including magnetic particles and the one or more analytes and having an RF coil disposed about the well, the RF coil configured to detect a signal by exposing the liquid sample to a bias homogenous magnetic field created using the permanent magnet and an RF pulse sequence; and (a3) one or more electrical elements in communication with the RF coil, the electrical elements configured to amplify, rectify, transmit, and/or digitize the signal; and (b) one or more second units including (b1) a permanent magnet adjacent a first sample position for holding a liquid sample and configured to apply a first gradient magnetic field to the liquid sample. The one or more second units can further include a second permanent magnet adjacent a second sample position for holding a liquid sample and configured to apply a second gradient magnetic field to the liquid sample, the second magnetic field aligned to apply a gradient magnetic field to the sample from a direction different from the direction of the first field gradient, and a means for moving a liquid sample from the first sample position to the second sample position. In certain embodiments, the one or more second units is incapable of measuring a signal (e.g., incapable of measuring an NMR relaxation rate), and/or lacks an RF coil, or a means for producing an RF pulse. In certain embodiments, the angle between the first direction and the second direction relative to the liquid sample is between 0° and 180° (e.g., from 0° to 10°, 5° to 120°, 20° to 60°, 30° to 80°, 45° to 90°, 60° to 120°, 80° to 135°, or from 120° to 180°). The system can further include a sample holder for holding the liquid sample and configured to move the liquid sample from the first position to the second position. In particular embodiments, the system includes an array of the one or more second units for assisting the agglomeration of an array of samples simultaneously. For example, the array can be configured to rotate one or more liquid from a first position in which a magnetic field is applied to the side of a sample to a second position in which a magnetic field is applied to the bottom of a sample. The system can include a cartridge unit, an agitation unit, a centrifuge, or any other system component described herein. For example, the system can further include (c) a third unit including a removable cartridge sized to facilitate insertion into and removal from the system and having a compartment including one or more populations of magnetic particles having binding moieties on their surfaces, wherein the binding moieties are operative to alter an aggregation of the magnetic particles in the presence of the one or more analytes. In particular embodiments, the removable cartridge is a modular cartridge including (i) a reagent module for holding one or more assay reagents; and (ii) a detection module including a detection chamber for holding a liquid sample including magnetic particles and one or more analytes, wherein the reagent module and the detection module can be assembled into the modular cartridge prior to use, and wherein the detection chamber is removable from the modular cartridge. The modular cartridge can further include an inlet module, wherein the inlet module, the reagent module, and the detection module can be assembled into the modular cartridge prior to use, and wherein the inlet module is sterilizable. In another embodiment, the system can further include a system computer with processor for implementing an assay protocol and storing assay data, and wherein the removable cartridge further includes (i) a readable label indicating the analyte to be detected, (ii) a readable label indicating the assay protocol to be implemented, (iii) a readable label indicating a patient identification number, (iv) a readable label indicating the position of assay reagents contained in the cartridge, or (v) a readable label including instructions for the programmable processor.

The invention further features a system for the detection of one or more analytes, the system including: (a) a first unit including (a1) a permanent magnet defining a magnetic field; (a2) a support defining a well for holding a liquid sample including magnetic particles and the one or more analytes and having an RF coil disposed about the well, the RF coil configured to detect a signal produced by exposing the liquid sample to a bias magnetic field created using the permanent magnet and an RF pulse sequence; and (a3) one or more electrical elements in communication with the RF coil, the electrical elements configured to amplify, rectify, transmit, and/or digitize the signal; and (b) a second unit including a removable cartridge sized to facilitate insertion into and removal from the system, wherein the removable cartridge is a modular cartridge including (i) a reagent module for holding one or more assay reagents; and (ii) a detection module including a detection chamber for holding a liquid sample including the magnetic particles and the one or more analytes, wherein the reagent module and the detection module can be assembled into the modular cartridge prior to use, and wherein the detection chamber is removable from the modular cartridge. The modular cartridge can further include an inlet module, wherein the inlet module, the reagent module, and the detection module can be assembled into the modular cartridge prior to use, and wherein the inlet module is sterilizable. In certain embodiments, the system further includes a system computer with processor for implementing an assay protocol and storing assay data, and wherein the removable cartridge further includes (i) a readable label indicating the analyte to be detected, (ii) a readable label indicating the assay protocol to be implemented, (iii) a readable label indicating a patient identification number, (iv) a readable label indicating the position of assay reagents contained in the cartridge, or (v) a readable label including instructions for the programmable processor. The system can include a cartridge unit, an agitation unit, a centrifuge, or any other system component described herein.

The invention features an agitation unit for the automated mixing of a liquid sample in a sample chamber, including a motor for providing a rotational driving force to a motor shaft coupled to a drive shaft, the driveshaft having a first end coupled to the motor shaft and a second end coupled to a plate bearing a sample holder for holding the sample chamber, the draft shaft including a first axis coaxial to the motor shaft, and a second axis that is offset and parallel to the motor shaft, such that the second axis of the driveshaft, the plate, and the sample holder are driven in an orbital path, wherein the motor includes an index mark and/or other position sensing means such as an optical, magnetic or resistive position encoder for positioning the sample chamber in a predetermined position following the mixing or a sensor which tracks the sample's position throughout its path.

The invention features a system for the detection of one or more analytes, the system including: (a) a first unit including (a1) a permanent magnet defining a magnetic field; (a2) a support defining a well for holding a liquid sample including magnetic particles and the one or more analytes and having an RF coil disposed about the well, the RF coil configured to detect a signal produced by exposing the liquid sample to a bias magnetic field created using the permanent magnet and an RF pulse sequence; and (a3) one or more electrical elements in communication with the RF coil, the electrical elements configured to amplify, rectify, transmit, and/or digitize the signal; and (b) a second unit for the automated mixing of a liquid sample in a sample chamber, including a motor for providing a rotational driving force to a motor shaft coupled to a drive shaft, the driveshaft having a first end coupled to the motor shaft and a second end coupled to a plate bearing a sample holder for holding the sample chamber, the draft shaft including a first axis coaxial to the motor shaft, and a second axis that is offset and parallel to the motor shaft, such that the second axis of the driveshaft, the plate, and the sample holder are driven in an orbital path, wherein the motor includes an index mark and/or other position sensing means such as an optical, magnetic or resistive position encoder for positioning the sample chamber in a predetermined position following the mixing or a sensor which tracks the sample's position throughout its path.

In certain embodiments, the system further includes a robotic arm for placing the sample chamber in, and removing the sample chamber from, the agitation unit.

The invention further features a system for the detection of one or more analytes, the system including: (a) a first unit including (a1) a permanent magnet defining a magnetic field; (a2) a support defining a well for holding a liquid sample including magnetic particles and the one or more analytes and having an RF coil disposed about the well, the RF coil configured to detect a signal produced by exposing the liquid sample to a bias magnetic field created using the permanent magnet and an RF pulse sequence; and (a3) one or more electrical elements in communication with the RF coil, the electrical elements configured to amplify, rectify, transmit, and/or digitize the signal; and (b) a centrifuge including a motor for providing a rotational driving force to a drive shaft, the drive shaft having a first end coupled to the motor and a second end coupled to a centrifuge rotor bearing a sample holder for holding the sample chamber, wherein the motor includes an index mark and/or other position sensing means such as an optical, magnetic or resistive position encoder for positioning the sample chamber in a predetermined position following the centrifuging of the sample or a sensor which tracks the sample's position throughout its path.

The invention further features a system for the detection of one or more analytes, the system including: (a) a disposable sample holder defining a well for holding a liquid sample and having an RF coil contained within the disposable sample holder and disposed about the well, the RF coil configured to detect a signal produced by exposing the liquid sample to a bias magnetic field created using the permanent magnet and an RF pulse sequence, wherein the disposable sample holder includes one or more fusable links; and (b) an MR reader including (b1) a permanent magnet defining a magnetic field; (b2) an RF pulse sequence and detection coil; (b3) one or more electrical elements in communication with the RF coil, the electrical elements configured to amplify, rectify, transmit, and/or digitize the signal; and (b4) one or more electrical elements in communication with the fusable link and configured to apply excess current to the fusable link, causing the link to break and rendering the coil inoperable following a predetermined working lifetime. In certain embodiments, the electrical element in communication with the RF coil is inductively coupled to the RF coil.

The invention features a system for the detection of creatinine, tacrolimus, and Candida, the system including: (a) a first unit including (a1) a permanent magnet defining a magnetic field; (a2) a support defining a well for holding a liquid sample including magnetic particles and the creatinine, tacrolimus, and Candida and having an RF coil disposed about the well, the RF coil configured to detect signal produced by exposing the liquid sample to a bias magnetic field created using the permanent magnet and an RF pulse sequence; and (a3) an electrical element in communication with the RF coil, the electrical element configured to amplify, rectify, transmit, and/or digitize the signal; and (b) a second unit including a removable cartridge sized to facilitate insertion into and removal from the system, wherein the removable cartridge is a modular cartridge including (i) a plurality of reagent modules for holding one or more assay reagents; and (ii) a plurality of detection module including a detection chamber for holding a liquid sample including the magnetic particles and the creatinine, tacrolimus, and Candida, wherein the plurality of reagent modules includes (i) a first population of magnetic particles having a mean diameter of from 150 nm to 699 nm (e.g., from 150 to 250, 200 to 350, 250 to 450, 300 to 500, 450 to 650, or from 500 to 699 nm), a T₂ relaxivity per particle of from 1×10⁸ to 1×10¹² mM⁻¹s⁻¹ (e.g., from 1×10⁸ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or from 1×10¹⁰ to 1×10¹² mM⁻¹s⁻¹), and creatinine antibodies conjugated to their surface; (ii) a multivalent binding agent bearing a plurality of creatinine conjugates designed to form aggregates with the first population of magnetic particles in the absence of creatinine; (iii) a second population of magnetic particles having a mean diameter of from 150 nm to 699 nm (e.g., from 150 to 250, 200 to 350, 250 to 450, 300 to 500, 450 to 650, or from 500 to 699 nm), a T₂ relaxivity per particle of from 1×10⁸ to 1×10¹² mM⁻¹s⁻¹ (e.g., from 1×10⁸ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or from 1×10¹⁰ to 1×10¹² mM⁻¹s⁻¹), and tacrolimus antibodies conjugated to their surface; (iv) a multivalent binding agent bearing a plurality of tacrolimus conjugates designed to form aggregates with the second population of magnetic particles in the absence of tacrolimus; (v) a third population of magnetic particles have a mean diameter of from 700 nm to 1200 nm (e.g., from 700 to 850, 800 to 950, 900 to 1050, or from 1000 to 1200 nm), a T₂ relaxivity per particle of from 1×10⁹ to 1×10¹² mM⁻¹s⁻¹ (e.g., from 1×10⁸ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or from 1×10¹⁰ to 1×10¹² mM⁻¹s⁻¹), and having a first probe and a second probe conjugated to their surface selected to form aggregates in the presence of a Candida nucleic acid, the first probe operative to bind to a first segment of the Candida nucleic acid and the second probe operative to bind to a second segment of the Candida nucleic acid. In certain embodiments, the magnetic particles are substantially monodisperse; exhibit nonspecific reversibility in the absence of the analyte and multivalent binding agent; and/or the magnetic particles further include a surface decorated with a blocking agent selected from albumin, fish skin gelatin, gamma globulin, lysozyme, casein, peptidase, and an amine-bearing moiety (e.g., amino polyethyleneglycol, glycine, ethylenediamine, or amino dextran). In particular embodiments, the liquid sample further includes a buffer, from 0.1% to 3% (w/w) albumin (e.g., from 0.1% to 0.5%, 0.3% to 0.7%, 0.5% to 1%, 0.8% to 2%, or from 1.5% to 3% (w/w) albumin), from 0.01% to 0.5% nonionic surfactant (e.g., from 0.01% to 0.05%, 0.05% to 0.1%, 0.05% to 0.2%, 0.1% to 0.3%, 0.2% to 0.4%, or from 0.3% to 0.5% nonionic surfactant), or a combination thereof. In still other embodiments, the magnetic particles include a surface decorated with 40 μg to 100 μg (e.g., 40 μg to 60 μg, 50 μg to 70 μg, 60 μg to 80 μg, or 80 μg to 100 μg,) of one or more proteins per milligram of the magnetic particles. The liquid sample can include a multivalent binding agent bearing a plurality of analytes conjugated to a polymeric scaffold. In another embodiment, the liquid sample includes from 1×10⁶ to 1×10¹³ of the magnetic particles per milliliter of the liquid sample (e.g., from 1×10⁶ to 1×10⁸, 1×10⁷ to 1×10⁸, 1×10⁷ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or 1×10¹⁰ to 1×10¹³ magnetic particles per milliliter).

The invention features a method for measuring the concentration of creatinine in a liquid sample, the method including: (a) contacting a solution with (i) magnetic particles to produce a liquid sample including from 1×10⁶ to 1×10¹³ magnetic particles per milliliter of the liquid sample (e.g., from 1×10⁶ to 1×10⁸, 1×10⁷ to 1×10⁸, 1×10⁷ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or 1×10¹⁰ to 1×10¹³ magnetic particles per milliliter), wherein the magnetic particles have a mean diameter of from 150 nm to 1200 nm (e.g., from 150 to 250, 200 to 350, 250 to 450, 300 to 500, 450 to 650, 500 to 700 nm, 700 to 850, 800 to 950, 900 to 1050, or from 1000 to 1200 nm), a T₂ relaxivity per particle of from 1×10⁸ to 1×10¹² mM⁻¹s⁻¹ (e.g., from 1×10⁸ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or from 1×10¹⁰ to 1×10¹² mM⁻¹s⁻¹), and creatinine antibodies conjugated to their surface, and (ii) a multivalent binding agent bearing a plurality of creatinine conjugates designed to form aggregates with the magnetic particles in the absence of creatinine; (b) placing the liquid sample in a device, the device including a support defining a well for holding the liquid sample including the magnetic particles, the multivalent binding agent, and the creatinine, and having an RF coil disposed about the well, the RF coil configured to detect a signal produced by exposing the liquid sample to a bias magnetic field created using one or more magnets and an RF pulse sequence; (c) exposing the sample to a bias magnetic field and an RF pulse sequence; (d) following step (c), measuring the signal; and (e) on the basis of the result of step (d), determining the concentration of creatinine in the liquid sample. In certain embodiments, the magnetic particles are substantially monodisperse; exhibit nonspecific reversibility in the absence of the analyte and multivalent binding agent; and/or the magnetic particles further include a surface decorated with a blocking agent selected from albumin, fish skin gelatin, gamma globulin, lysozyme, casein, peptidase, and an amine-bearing moiety (e.g., amino polyethyleneglycol, glycine, ethylenediamine, or amino dextran). In particular embodiments, the liquid sample further includes a buffer, from 0.1% to 3% (w/w) albumin (e.g., from 0.1% to 0.5%, 0.3% to 0.7%, 0.5% to 1%, 0.8% to 2%, or from 1.5% to 3% (w/w) albumin), from 0.01% to 0.5% nonionic surfactant (e.g., from 0.01% to 0.05%, 0.05% to 0.1%, 0.05% to 0.2%, 0.1% to 0.3%, 0.2% to 0.4%, or from 0.3% to 0.5% nonionic surfactant), or a combination thereof. In still other embodiments, the magnetic particles include a surface decorated with 40 μg to 100 μg (e.g., 40 μg to 60 μg, 50 μg to 70 μg, 60 μg to 80 μg, or 80 μg to 100 μg,) of one or more proteins per milligram of the magnetic particles. The liquid sample can include a multivalent binding agent bearing a plurality of analytes conjugated to a polymeric scaffold.

The invention features a multivalent binding agent including two or more creatinine moieties covalently linked to a scaffold. In certain embodiments, the multivalent binding agent is a compound of formula (I): (A)_(n)-(B)  (I) wherein (A) is

(B) is a polymeric scaffold covalently attached to each (A), m is an integer from 2 to 10, and n is an integer from 2 to 50.

The invention features a solution including from 1×10⁶ to 1×10¹³ magnetic particles per milliliter of the solution (e.g., from 1×10⁶ to 1×10⁸, 1×10⁷ to 1×10⁸, 1×10⁷ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or 1×10¹⁰ to 1×10¹³ magnetic particles per milliliter), wherein the magnetic particles have a mean diameter of from 150 nm to 600 nm (e.g., from 150 to 250, 200 to 350, 250 to 450, 300 to 500, 450 to 650, or from 500 to 600 nm), a T₂ relaxivity per particle of from 1×10⁸ to 1×10¹² mM⁻¹s⁻¹ (e.g., from 1×10⁸ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or from 1×10¹⁰ to 1×10¹² mM⁻¹s⁻¹), and a surface bearing creatinine conjugate (A), wherein (A) is selected from:

and m is an integer from 2 to 10.

The invention further features solution including from 1×10⁶ to 1×10¹³ magnetic particles per milliliter of the solution (e.g., from 1×10⁶ to 1×10⁸, 1×10⁷ to 1×10⁸, 1×10⁷ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or 1×10¹⁰ to 1×10¹³ magnetic particles per milliliter), wherein the magnetic particles have a mean diameter of from 150 nm to 600 nm (e.g., from 150 to 250, 200 to 350, 250 to 450, 300 to 500, 450 to 650, or from 500 to 600 nm), a T₂ relaxivity per particle of from 1×10⁸ to 1×10¹² mM⁻¹s⁻¹ (e.g., from 1×10⁸ to 1×10⁹, 1×10 ⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or from 1×10¹⁰ to 1×10¹² mM¹s⁻¹), and a surface bearing antibodies having affinity for the creatinine conjugate:

wherein (B) is a polymeric scaffold.

The invention further features a method for measuring the concentration of tacrolimus in a liquid sample, the method including: (a) contacting a solution with (i) magnetic particles to produce a liquid sample including from 1×10⁶ to 1×10¹³ magnetic particles per milliliter of the liquid sample (e.g., from 1×10⁶ to 1×10⁸, 1×10⁷ to 1×10⁸, 1×10⁷ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or 1×10¹⁰ to 1×10¹³ magnetic particles per milliliter), wherein the magnetic particles have a mean diameter of from 150 nm to 1200 nm (e.g., from 150 to 250, 200 to 350, 250 to 450, 300 to 500, 450 to 650, 500 to 700 nm, 700 to 850, 800 to 950, 900 to 1050, or from 1000 to 1200 nm), a T₂ relaxivity per particle of from 1×10⁸ to 1×10¹² mM⁻¹s⁻¹ (e.g., from 1×10⁸ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or from 1×10¹⁰ to 1×10¹² mM⁻¹s⁻¹), and tacrolimus antibodies conjugated to their surface, and (ii) a multivalent binding agent bearing a plurality of tacrolimus conjugates designed to form aggregates with the magnetic particles in the absence of tacrolimus; (b) placing the liquid sample in a device, the device including a support defining a well for holding the liquid sample including the magnetic particles, the multivalent binding agent, and the tacrolimus, and having an RF coil disposed about the well, the RF coil configured to detect a signal produced by exposing the liquid sample to a bias magnetic field created using one or more magnets and an RF pulse sequence; (c) exposing the sample to a bias magnetic field and an RF pulse sequence; (d) following step (c), measuring the signal; and (e) on the basis of the result of step (d), determining the concentration of tacrolimus in the liquid sample. In certain embodiments, the magnetic particles are substantially monodisperse; exhibit nonspecific reversibility in the absence of the analyte and multivalent binding agent; and/or the magnetic particles further include a surface decorated with a blocking agent selected from albumin, fish skin gelatin, gamma globulin, lysozyme, casein, peptidase, and an amine-bearing moiety (e.g., amino polyethyleneglycol, glycine, ethylenediamine, or amino dextran). In particular embodiments, the liquid sample further includes a buffer, from 0.1% to 3% (w/w) albumin (e.g., from 0.1% to 0.5%, 0.3% to 0.7%, 0.5% to 1%, 0.8% to 2%, or from 1.5% to 3% (w/w) albumin), from 0.01% to 0.5% nonionic surfactant (e.g., from 0.01% to 0.05%, 0.05% to 0.1%, 0.05% to 0.2%, 0.1% to 0.3%, 0.2% to 0.4%, or from 0.3% to 0.5% nonionic surfactant), or a combination thereof. In still other embodiments, the magnetic particles include a surface decorated with 40 μg to 100 μg (e.g., 40 μg to 60 μg, 50 μg to 70 μg, 60 μg to 80 μg, or 80 μg to 100 μg,) of one or more proteins per milligram of the magnetic particles. The liquid sample can include a multivalent binding agent bearing a plurality of analytes conjugated to a polymeric scaffold.

The invention features a multivalent binding agent including two or more tacrolimus moieties, including tacrolimus metabolites described herein or structurally similar compounds for which the antibody has affinity covalently linked to a scaffold. In certain embodiments, the multivalent binding agent is a compound of formula (II): (A)_(n)-(B)  (II) wherein (A) is

(B) is a polymeric scaffold covalently attached to each (A), and n is an integer from 2 to 50.

The invention features a solution including from 1×10⁶ to 1×10¹³ magnetic particles per milliliter of the solution (e.g., from 1×10⁶ to 1×10⁸, 1×10⁷ to 1×10⁸, 1×10⁷ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or 1×10¹⁰ to 1×10¹³ magnetic particles per milliliter), wherein the magnetic particles have a mean diameter of from 150 nm to 600 nm (e.g., from 150 to 250, 200 to 350, 250 to 450, 300 to 500, 450 to 650, or from 500 to 600 nm), a T₂ relaxivity per particle of from 1×10⁸ to 1×10¹² mM⁻¹s⁻¹(e.g., from 1×10⁸ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or from 1×10¹⁰ to 1×10¹² mM⁻¹s⁻¹), and a surface bearing antibodies having affinity for the tacrolimus conjugate:

wherein (B) is a polymeric scaffold.

In an embodiment of any of the above solutions, (i) the magnetic particles are substantially monodisperse; (ii) the magnetic particles exhibit nonspecific reversibility in plasma; (iii) the magnetic particles further include a surface decorated with a blocking agent selected from albumin, fish skin gelatin, gamma globulin, lysozyme, casein, peptidase, and an amine-bearing moiety (e.g., amino polyethyleneglycol, glycine, ethylenediamine, or amino dextran); (iv) the liquid sample further includes a buffer, from 0.1% to 3% (w/w) albumin (e.g., from 0.1% to 0.5%, 0.3% to 0.7%, 0.5% to 1%, 0.8% to 2%, or from 1.5% to 3% (w/w) albumin), from 0.01% to 0.5% nonionic surfactant (e.g., from 0.01% to 0.05%, 0.05% to 0.1%, 0.05% to 0.2%, 0.1% to 0.3%, 0.2% to 0.4%, or from 0.3% to 0.5% nonionic surfactant), or a combination thereof; and/or (iv) the magnetic particles include a surface decorated with 40 μg to 100 μg (e.g., 40 μg to 60 μg, 50 μg to 70 μg, 60 μg to 80 μg, or 80 μg to 100 μg,) of one or more proteins per milligram of the magnetic particles. The solutions can be used in any of the systems or methods described herein.

The invention features a removable cartridge sized to facilitate insertion into and removal from a system of the invention, wherein the removable cartridge includes one or more chambers for holding a plurality of reagent modules for holding one or more assay reagents, wherein the reagent modules include (i) a chamber for holding from 1×10⁶ to 1×10¹³ magnetic particles (e.g., from 1×10⁶ to 1×10⁸, 1×10⁷ to 1×10⁸, 1×10⁷ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or 1×10¹⁰ to 1×10¹³ magnetic particles) having a mean diameter of from 100 nm to 699 nm (e.g., from 150 to 250, 200 to 350, 250 to 450, 300 to 500, 450 to 650, or from 500 to 699 nm), a T₂ relaxivity per particle of from 1×10⁸ to 1×10¹² mM⁻¹s⁻¹ (e.g., from 1×10⁸ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or from 1×10¹⁰ to 1×10¹² mM⁻¹s⁻¹), and binding moieties on their surfaces, the binding moieties operative to alter the specific aggregation of the magnetic particles in the presence of the one or more analytes or a multivalent binding agent; and (ii) a chamber for holding a buffer. In a related aspect, the invention features a removable cartridge sized to facilitate insertion into and removal from a system of the invention, wherein the removable cartridge comprises one or more chambers for holding a plurality of reagent modules for holding one or more assay reagents, wherein the reagent modules include (i) a chamber for holding from 1×10⁶ to 1×10¹³ magnetic particles (e.g., from 1×10⁶ to 1×10⁸, 1×10⁷ to 1×10⁸, 1×10⁷ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or 1×10¹⁰ to 1×10¹³ magnetic particles) having a mean diameter of from 700 nm to 1200 nm (e.g., from 700 to 850, 800 to 950, 900 to 1050, or from 1000 to 1200 nm), a T₂ relaxivity per particle of from 1×10⁹ to 1×10¹² mM⁻¹s⁻¹ (e.g., from 1×10⁹ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, or from 1×10¹⁰ to 1×10¹² mM⁻¹s⁻¹), and oligonucleotide binding moieties on their surfaces, the oligonucleotide binding moieties operative to alter the specific aggregation of the magnetic particles in the presence of the one or more analytes; and (ii) a chamber for holding a buffer. The magnetic particles can be any described herein, decorated with any binding moieties described herein, for detecting any analyte described herein. In particular embodiments of the removable cartridges, the magnetic particles and buffer are together in a single chamber within the cartridge. In still other embodiments, the buffer includes from 0.1% to 3% (w/w) albumin, from 0.01% to 0.5% nonionic surfactant, a lysis agent, or a combination thereof. The removable cartridge can further include a chamber including beads for lysing cells; a chamber including a polymerase; and/or a chamber including a primer.

The invention features a removable cartridge sized to facilitate insertion into and removal from a system of the invention, wherein the removable cartridge includes one or more chambers for holding a plurality of reagent modules for holding one or more assay reagents, wherein the reagent modules include (i) a chamber for holding from 1×10⁸ to 1×10¹⁰ magnetic particles having a mean diameter of from 100 nm to 350 nm, a T₂ relaxivity per particle of from 5×10⁸ to 1×10¹⁰ mM⁻¹s⁻¹, and binding moieties on their surfaces (e.g., antibodies, conjugated analyte), the binding moieties operative to alter the specific aggregation of the magnetic particles in the presence of the one or more analytes or a multivalent binding agent; and (ii) a chamber for holding a buffer including from 0.1% to 3% (w/w) albumin (e.g., from 0.1% to 0.5%, 0.3% to 0.7%, 0.5% to 1%, 0.8% to 2%, or from 1.5% to 3% (w/w) albumin), from 0.01% to 0.5% nonionic surfactant (e.g., from 0.01% to 0.05%, 0.05% to 0.1%, 0.05% to 0.2%, 0.1% to 0.3%, 0.2% to 0.4%, or from 0.3% to 0.5% nonionic surfactant), or a combination thereof. In one embodiment, the magnetic particles and buffer are together in a single chamber within the cartridge.

In any of the systems, kits, cartridges, and methods of the invention, the liquid sample can include from 1×10⁸ to 1×10¹⁰ magnetic particles having a mean diameter of from 100 nm to 350 nm, a T₂ relaxivity per particle of from 5×10⁸ to 1×10¹⁰ mM⁻¹s⁻¹, and binding moieties on their surfaces (e.g., antibodies, conjugated analyte), the binding moieties operative to alter the specific aggregation of the magnetic particles in the presence of the one or more analytes or a multivalent binding agent.

In any of the systems, kits, cartridges, and methods of the invention for detection of any analyte in a whole blood sample, the disruption of the red blood cells can be carried out using an erythrocyte lysis agent (i.e., a lysis buffer, or a nonionic detergent). Erythrocyte lysis buffers which can be used in the methods of the invention include, without limitation, isotonic solutions of ammonium chloride (optionally including carbonate buffer and/or EDTA), and hypotonic solutions. Alternatively, the erythrocyte lysis agent can be an aqueous solution of nonionic detergents (e.g., nonyl phenoxypolyethoxylethanol (NP-40), 4-octylphenol polyethoxylate (Triton-X100), Brij-58, or related nonionic surfactants, and mixtures thereof). The erythrocyte lysis agent disrupts at least some of the red blood cells, allowing a large fraction of certain components of whole blood (e.g., certain whole blood proteins) to be separated (e.g., as supernatant following centrifugation) from the white blood cells, yeast cells, and/or bacteria cells present in the whold blood sample. Following Erythrocyte lysis and centrifugation, the resulting pellet is reconstituted to form an extract.

The methods, kits, cartridges, and systems of the invention can be configured to detect a predetermined panel of pathogen-associated analytes. For example, the panel can be a candida fungal panel configured to individually detect three or more of Candida guilliermondii, C. albicans, C. glabrata, C. krusei, C. Lusitaniae, C. parapsilosis, and C. tropicalis. In another embodiment, the panel can be a bacterial panel configured to individually detect three or more of coagulase negative Staphylococcus, Enterococcus faecalis, E. faecium, Pseudomonas aeruginosa, Staphylococcus aureus, and Escherichia coli. In a particular embodiment, the panel can be a viral panel configured to individually detect three or more of Cytomegalovirus (CMV), Epstein Barr Virus, BK Virus, Hepatitis B virus, Hepatitis C virus, Herpes simplex virus (HSV), HSV1, HSV2, Respiratory syncytial virus (RSV), Influenza; Influenza A, Influenza A subtype H1, Influenza A subtype H3, Influenza B, Human Herpes Virus 6, Human Herpes Virus 8, Human Metapneumovirus (hMPV), Rhinovirus, Parainfluenza 1, Parainfluenza 2, Parainfluenza 3, and Adenovirus. The panel can be a bacterial panel configured to individually detect three or more of E. coli, CoNS (coagulase negative staph), Pseudomonas aeruginosa, S. aureus, E. faecium, E. faecalis, and Klebsiella pneumonia. The panel can be a bacterial panel configured to individually detect three or more of A. fumigates, and A. flavum. The panel can be a bacterial panel configured to individually detect three or more of Acinetobacter baumannii, Enterobacter aeraogenes, Enterobacter cloacae, Klebsiella oxytoca, Proteus mirabilis, Serratia marcescens, Staphylococcus haemolyticus, Stenotro-phomonas maltophilia, Streptococcus agalactie, Streptococcus mitis, Streptococcus pneumonia, and Streptococcus pyogenes. The panel can be a meningitis panel configured to individually detect three or more of Streptococcus pneumonia, H. influenza, Neisseria Meningitis, HSV1, HSV2, Enterovirus, Listeria, E. coli, Group B Streptococcus. The panel can be configured to individually detect three or more of N. gonnorrhoeae, S. aureus, S. pyogenes, CoNS, and Borrelia burgdorferi. The panel can be configured to individually detect three or more of C. Difficile, Toxin A, and Toxin B. The panel can be a pneumonia panel configured to individually detect three or more of Streptococcus pneumonia, MRSA, Legionella, C. pneumonia, and Mycoplasma Pneumonia. The panel can be configured to individually detect three or more of treatment resistant mutations selected from mecA, vanA, vanB, NDM-1, KPC, and VIM. The panel can be configured to individually detect three or more of H. influenza, N. gonnorrhoeae, H. pylori, Campylobacter, Brucella, Legionella, and Stenotrophomonas maltophilia. The panel can be configured to detect total viral load caused by CMV, EBV, BK Virus, HIV, HBV, and HCV. The panel can be configured to detect fungal load and/or bacterial load. Viral load determination can be using a standard curve and measuring the sample against this standard curve or some other method of quantitation of the pathogen in a sample. The quantitative measuring method may include real-time PCR, competitive PCR (ratio of two cometiting signals) or other methods mentioned here. The panel can be configured to detect immune response in a subject by monitoring PCT, MCP-1, CRP, GRO-alpha, High mobility group-box 1 protein (HMBG-1), IL-1 receptor, IL-1 receptor antagonist, IL-1b, IL-2, IL-4, IL-6, IL-8, IL-10, IL-12, IL-13, IL-18, macrophage inflammatory protein (MIP-1), macrophage migration inhibitory factor (MIF), osteopontin, RANTES (regulated on activation, normal T-cell expressed and secreted; or CCL5), Th1, Th17, and/or TNF-α. The panel can be configured to individually detect three or more of Ehrlichea, Mycobacterium, Syphillis, Borrelia burgdorferi, Cryptococcus, Histoplasma, and Blastomyces. The panel can be an influenza panel configured to individually detect three or more of Influenza A, Influenza B, RSV, Parainfluenza, Meta-pneumovirus, Rhinovirus, and Adenovirus.

The methods, kits, cartridges, and systems of the invention can be configured to reduce sample to sample variablility by determining a magnetic resonance signal prior to and after hybridization. The addition of derivatized nanoparticles to the sample prior to methods to enhance clustering may provide a baseline, internal T₂ signal that can either be subtracted or used to modify the T₂ signal after analyte-derivatized particle binding and clustering. This method may also be used to determine or manage cartridge to cartridge variability.

The terms “aggregation,” “agglomeration,” and “clustering” are used interchangeably in the context of the magnetic particles described herein and mean the binding of two or more magnetic particles to one another, e.g., via a multivalent analyte, multimeric form of analyte, antibody, nucleic acid molecule, or other binding molecule or entity. In some instances, magnetic particle agglomeration is reversible.

By “analyte” is meant a substance or a constituent of a sample to be analyzed. Exemplary analytes include one or more species of one or more of the following: a protein, a peptide, a polypeptide, an amino acid, a nucleic acid, an oligonucleotide, RNA, DNA, an antibody, a carbohydrate, a polysaccharide, glucose, a lipid, a gas (e.g., oxygen or carbon dioxide), an electrolyte (e.g., sodium, potassium, chloride, bicarbonate, BUN, magnesium, phosphate, calcium, ammonia, lactate), a lipoprotein, cholesterol, a fatty acid, a glycoprotein, a proteoglycan, a lipopolysaccharide, a cell surface marker (e.g., CD3, CD4, CD8, IL2R, or CD35), a cytoplasmic marker (e.g., CD4/CD8 or CD4/viral load), a therapeutic agent, a metabolite of a therapeutic agent, a marker for the detection of a weapon (e.g., a chemical or biological weapon), an organism, a pathogen, a pathogen byproduct, a parasite (e.g., a protozoan or a helminth), a protist, a fungus (e.g., yeast or mold), a bacterium, an actinomycete, a cell (e.g., a whole cell, a tumor cell, a stem cell, a white blood cell, a T cell (e.g., displaying CD3, CD4, CD8, IL2R, CD35, or other surface markers), or another cell identified with one or more specific markers), a virus, a prion, a plant component, a plant by-product, algae, an algae by-product, plant growth hormone, an insecticide, a man-made toxin, an environmental toxin, an oil component, and components derived therefrom. As used herein, the term “small molecule” refers to a drug, medication, medicament, or other chemically synthesized compound that is contemplated for human therapeutic use. As used herein, the term “biologic” refers to a substance derived from a biological source, not synthesized and that is contemplated for human therapeutic use. A “biomarker” is a biological substance that can be used as an indicator of a particular disease state or particular physiological state of an organism, generally a biomarker is a protein or other native compound measured in bodily fluid whose concentration reflects the presence or severity or staging of a disease state or dysfunction, can be used to monitor therapeutic progress of treatment of a disease or disorder or dysfunction, or can be used as a surrogate measure of clinical outcome or progression. As used herein, the term “metabolic biomarker” refers to a substance, molecule, or compound that is synthesized or biologically derived that is used to determine the status of a patient or subject's liver or kidney function. As used herein, the term “genotyping” refers to the ability to determine genetic differences in specific genes that may or may not affect the phenotype of the specific gene. As used herein, the term “phenotype” refers to the resultant biological expression, (metabolic or physiological) of the protein set by the genotype. As used herein, the term “gene expression profiling” refers to the ability to determine the rate or amount of the production of a gene product or the activity of gene transcription in a specific tissue, in a temporal or spatial manner. As used herein, the term “proteomic analysis” refers to a protein pattern or array to identify key differences in proteins or peptides in normal and diseased tissues. Additional exemplary analytes are described herein. The term analyte further includes components of a sample that are a direct product of a biochemical means of amplification of the initial target analyte, such as the product of a nucleic acid amplification reaction.

By an “isolated” nucleic acid molecule is meant a nucleic acid molecule that is removed from the environment in which it naturally occurs. For example, a naturally-occurring nucleic acid molecule present in the genome of cell or as part of a gene bank is not isolated, but the same molecule, separated from the remaining part of the genome, as a result of, e.g., a cloning event, amplification, or enrichment, is “isolated.” Typically, an isolated nucleic acid molecule is free from nucleic acid regions (e.g., coding regions) with which it is immediately contiguous, at the 5′ or 3′ ends, in the naturally occurring genome. Such isolated nucleic acid molecules can be part of a vector or a composition and still be isolated, as such a vector or composition is not part of its natural environment.

As used herein, “linked” means attached or bound by covalent bonds, non-covalent bonds, and/or linked via Van der Waals forces, hydrogen bonds, and/or other intermolecular forces.

The term “magnetic particle” refers to particles including materials of high positive magnetic susceptibility such as paramagnetic compounds, superparamagnetic compounds, and magnetite, gamma ferric oxide, or metallic iron.

As used herein, “nonspecific reversibility” refers to the colloidal stability and robustness of magnetic particles against non-specific aggregation in a liquid sample and can be determined by subjecting the particles to the intended assay conditions in the absence of a specific clustering moiety (i.e., an analyte or an agglomerator). For example, nonspecific reversibility can be determined by measuring the T₂ values of a solution of magnetic particles before and after incubation in a uniform magnetic field (defined as <5000 ppm) at 0.45 T for 3 minutes at 37° C. Magnetic particles are deemed to have nonspecific reversibility if the difference in T₂ values before and after subjecting the magnetic particles to the intended assay conditions vary by less than 10% (e.g., vary by less than 9%, 8%, 6%, 4%, 3%, 2%, or 1%). If the difference is greater than 10%, then the particles exhibit irreversibility in the buffer, diluents, and matrix tested, and manipulation of particle and matrix properties (e.g., coating and buffer formulation) may be required to produce a system in which the particles have nonspecific reversibility. In another example, the test can be applied by measuring the T₂ values of a solution of magnetic particles before and after incubation in a gradient magnetic field 1 Gauss/mm-10000 Gauss/mm.

As used herein, the term “NMR relaxation rate” refers to a measuring any of the following in a sample T₁, T₂, T₁/T₂ hybrid, T_(1rho), T_(2rho), and T₂*. The systems and methods of the invention are designed to produce an NMR relaxation rate characteristic of whether an analyte is present in the liquid sample. In some instances the NMR relaxation rate is characteristic of the quantity of analyte present in the liquid sample.

As used herein, the term “T₁/T₂ hybrid” refers to any detection method that combines a T₁ and a T₂ measurement. For example, the value of a T₁/T₂ hybrid can be a composite signal obtained through the combination of, ratio, or difference between two or more different T₁ and T₂ measurements. The T₁/T₂ hybrid can be obtained, for example, by using a pulse sequence in which T₁ and T₂ are alternatively measured or acquired in an interleaved fashion. Additionally, the T₁/T₂ hybrid signal can be acquired with a pulse sequence that measures a relaxation rate that is comprised of both T₁ and T₂ relaxation rates or mechanisms.

A “pathogen” means an agent causing disease or illness to its host, such as an organism or infectious particle, capable of producing a disease in another organism, and includes but is not limited to bacteria, viruses, protozoa, prions, yeast and fungi or pathogen by-products. “Pathogen by-products” are those biological substances arising from the pathogen that can be deleterious to the host or stimulate an excessive host immune response, for example pathogen antigen/s, metabolic substances, enzymes, biological substances, or toxins.

By “pathogen-associated analyte” is meant an analyte characteristic of the presence of a pathogen (e.g., a bacterium, fungus, or virus) in a sample. The pathogen-associated analyte can be a particular substance derived from a pathogen (e.g., a protein, nucleic acid, lipid, polysaccharide, or any other material produced by a pathogen) or a mixture derived from a pathogen (e.g., whole cells, or whole viruses). In certain instances, the pathogen-associated analyte is selected to be characteristic of the genus, species, or specific strain of pathogen being detected. Alternatively, the pathogen-associated analyte is selected to ascertain a property of the pathogen, such as resistance to a particular therapy. For example, the pathogen-associated analyte can be a gene, such as a Van A gene or Van B gene, characteristic of vancomycin resistance in a number of different bacterial species.

By “pulse sequence” or “RF pulse sequence” is meant one or more radio frequency pulses to be applied to a sample and designed to measure, e.g., certain NMR relaxation rates, such as spin echo sequences. A pulse sequence may also include the acquisition of a signal following one or more pulses to minimize noise and improve accuracy in the resulting signal value.

As used herein, the term “signal” refers to an NMR relaxation rate, frequency shift, susceptibility measurement, diffusion measurement, or correlation measurements.

As used herein, reference to the “size” of a magnetic particle refers to the average diameter for a mixture of the magnetic particles as determined by microscopy, light scattering, or other methods.

As used herein, the term “substantially monodisperse” refers to a mixture of magnetic particles having a polydispersity in size distribution as determined by the shape of the distribution curve of particle size in light scattering measurements. The FWHM (full width half max) of the particle distribution curve less than 25% of the peak position is considered substantially monodisperse. In addition, only one peak should be observed in the light scattering experiments and the peak position should be within one standard deviation of a population of known monodisperse particles.

By “T₂ relaxivity per particle” is meant the average T₂ relaxivity per particle in a population of magnetic particles.

As used herein, “unfractionated” refers to an assay in which none of the components of the sample being tested are removed following the addition of magnetic particles to the sample and prior to the NMR relaxation measurement.

It is contemplated that units, systems, methods, and processes of the claimed invention encompass variations and adaptations developed using information from the embodiments described herein. Throughout the description, where units and systems are described as having, including, or including specific components, or where processes and methods are described as having, including, or including specific steps, it is contemplated that, additionally, there are units and systems of the present invention that consist essentially of, or consist of, the recited components, and that there are processes and methods according to the present invention that consist essentially of, or consist of, the recited processing steps. It should be understood that the order of steps or order for performing certain actions is immaterial, unless otherwise specified, so long as the invention remains operable. Moreover, in many instances two or more steps or actions may be conducted simultaneously.

Other features and advantages of the invention will be apparent from the following detailed description, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic diagram of an NMR unit for detection of a signal response of a sample to an RF pulse sequence, according to an illustrative embodiment of the invention.

FIG. 1B depicts a typical coil configuration surrounding a sample tube for measuring a relaxation signal in a 20 μL sample.

FIGS. 2A-2E illustrate micro coil geometries which can be used in NMR (for excitation and/or detection); designs include, but are not limited to a wound solenoid coil (FIG. 2A), a planar coil (FIG. 2B), a MEMS solenoid coil (FIG. 2C), a MEMS Helmholz coil (FIG. 2D), and a saddle coil (FIG. 2E), according to an illustrative embodiment of the invention. Three dimensional lithographic coil fabrication of well characterized coils used in MR detection is also established and can be used for these applications, Demas et al. “Electronic characterization of lithographically patterned microcoils for high sensitivity NMR detection” J Magn Reson 200:56 (2009).

FIG. 3 is a drawing depicting an aggregation assay of the invention. The magnetic particles (dots) are coated with a binding agent (i.e., antibody, oligo, etc.) such that in the presence of analyte, or multivalent binding agent, aggregates are formed. The dotted circles represent the diffusion sphere or portion of the total fluid volume that a solution molecule may experience via its diffusion during a T₂ measurement (the exact path traveled by a water molecule is random, and this drawing is not to scale). Aggregation (right hand side) depletes portions of the sample from the microscopic magnetic non-uniformities that disrupt the water's T₂ signal, leading to an increase in T₂ relaxation.

FIGS. 4A-4E are a series of graphs depicting the dependence of transverse relaxivity (R₂) (FIG. 4A) or T2 (FIGS. 4B-4E) on particle diameter and particle aggregation. FIG. 4A is a graph depicting the motional averaging regime (light line, left side); the R₂ (1/T₂) measured by a CPMG sequence increases as particle size increases because the refocusing pulses are ineffective to counteract the dephasing effects of the particles. As the system transitions to the visit limited regime (dark line, right side) the refocusing pulses begin to become effective and the R₂ decreases as particle size increases. For homogeneous magnetic fields, the R₂* in the motional averaging regime matches the R₂ and the R₂* reaches a constant value in the visit limited regime. In a homogenous field, when the R₂* is less than the R₂ of either the motional averaging regime or visit limited regime the system is in the static dephasing regime. The empty circle represents the R₂ of a solution of 100% dispersed particles (diameter=15 nm) and the solid circle represents a solution of 100% clustered particles (diameter=200 nm). This is an example of how to interpret these curves for clustering reactions. The conditions for this curve are 0.1 mM Fe, Δω=8.85×10⁶, D=2.5×10⁻⁵ m²/s, and τ_(CP)=0.25 ms. FIG. 4B is a graph depicting the same light and dark curves plotted in terms of T₂ and diameter, on a linear scale. In this figure the black dashed line represents the T₂* measured in a non-uniform magnetic field where T₂* is always lower than T₂ and doesn't reflect the particle size. The data points are the same as well. FIG. 4C is a graph depicting the monodisperse clustering model and showing that T₂ will follow the curve as analyte is added because the average diameter of the population particles will cover all intermediate diameters between the initial and final states. FIG. 4D is a graph depicting the polydisperse model and showing that the T₂ will transition between the two points on this curve when particles form clusters of specific sizes. The response curve will be linear with regard to analyte addition, but non-linear with regard to volume fraction of clusters, because particles transition between state 1 and state 2. The slope of the response curve is directly proportional to the sensitivity of the assay. FIG. 4E is a graph showing the two regimes for particle aggregation and T₂ affects based on particle size and how clustering assays in the different regimes map onto the T₂ versus diameter curves (i) for the motional averaging regime T₂ decreases when particles cluster; and (ii) for the slow motion regime T₂ increases when particles cluster. Under the conditions shown in these models, the boundary between the two regimes is ca. 100 nm diameter particles. When small magnetic particles form aggregates under 100 nm in diameter, the result is a decrease in T₂ upon aggregate formation. When magnetic particles at or above 100 nm in diameter form larger aggregates, the result is an increase in T₂ upon aggregate formation.

FIGS. 5A-5C are drawings depicting different assay formats for the assays of the invention. FIG. 5A depicts an agglomerative sandwich immunoassay in which two populations of magnetic particles are designed to bind to two different epitopes of an analyte. FIG. 5B depicts a competitive immunoassay in which analyte in a liquid sample binds to a multivalent binding agent (a multivalent antibody), thereby inhibiting aggregation. FIG. 5C depicts a hybridization-mediated agglomerative assay in which two populations of particles are designed to bind to the first and second portions of a nucleic acid target, respectively.

FIG. 6 illustrates a modular cartridge concept in sections that can be packaged and stored separately. This is done, for example, so that the inlet module (shown elevated with inverted Vacutainer tube attached) can be sterilized while the reagent holding module in the middle is not. This allows the component containing reagents to be the only refrigerated component.

FIGS. 7A-7F depict a Vacutainer inlet module. FIG. 7A shows it in the inverted position after the user has removed the closure from the Vacutainer tube and placed the cartridge onto it. FIG. 7B shows the molded in path that the blood will follow out of the Vacutainer and into the sample loading region once the cartridge is turned right side up. The foil seal can be the bottom side of the channels, forming an inexpensively molded part with closed channels. FIG. 7C is a cutaway view showing the vent tube which allows air to enter into the vial as the blood leaves and fills the sample region. FIGS. 7D-7F depict an inlet module for sample aliquoting designed to interface with uncapped vacutainer tubes, and to aliquot two a sample volume that can be used to perform, for example, a candida assay. The inlet module has two hard plastic parts, that get ultrasonically welded together and foil sealed to form a network of channels to allow a flow path to form into the first well overflow to the second sample well. A soft vacutainer seal part is used to for a seal with the vacutainer. It has a port for sample flow, and a venting port, to allow the flow to occur.

FIG. 8 depicts the sample inlet module with the foil seal removed. On the top, one can see the small air inlet port to the left, the larger sample well in the center and a port which connects them together. This port provides a channel through which air can flow once the foil seal is pierced. It also provides an overflow into the body of the module to allow excess blood to drain away and not spill over. This effectively meters the blood sample to the volume contained in the sample well.

FIGS. 9A-9C depict a reagent module. FIG. 9A depicts the module of the cartridge that is intended to hold reagents and consumables for use during the assay. On the left are sealed pre-dispensed aliquots of reagents. On the right is a 2.8 ml conical bottomed centrifuge tube that is used for initial centrifugation of the blood. The other holes can be filled as need with vials, microcentrifuge tubes, and pipette tips. FIG. 9B is a cutaway view of the reagent module showing the holders for the pre-aliquoted reagent tips, including the feature at the bottom into which the tips are pressed to provide a seal. FIG. 9C depicts three representative pipette tips into which reagents can be pre-dispensed, and then the backs sealed. The tips are pressed into the sample holder to provide a seal.

FIGS. 10A and 10B depict an alternative design of the modular cartridge, showing a detection module with a recessed well for use in assays that require PCR. Cross-contamination from PCR products is controlled in two ways. First, the seals that are on the detection tubes are designed to seal to a pipette tip as it penetrates. Second, the instrument provides air flow through the recessed well by means of holes in the well to ensure that any aerosol is carried down and does not travel throughout the machine.

FIG. 11 depicts a detection module of cartridge showing detection tubes and one of the holes used to ensure air flow down and over the tubes during pipetting to help prevent aerosol escape.

FIG. 12 depicts a bottom view of the detection module, showing the bottom of the detection tubes and the two holes used to ensure airflow. An optional filter can be inserted here to capture any liquid aerosol and prevent it from entering the machine. This filter could also be a sheet of a hydrophobic material like Gore-tex that will allow air but not liquids to escape.

FIGS. 13A-13C depict a detection tube. FIG. 13A is a view of the detection tube. The tube itself could be an off the shelf 200 microliter PCR tube, while the cap is a custom molded elastomer part that provides a pressure resistant duckbill seal on the inside and a first seal to the pipette tip from the top. The seal is thus a make-break type of seal, where one seal is made before the other is broken. FIG. 13B depicts the custom molded seal component. Note the circular hole into which the pipette tip is inserted and the duckbill seal below, which provides a second seal that resists pressure developed in the tube. FIG. 13C depicts the seal showing the duckbill at bottom and the hole at top.

FIGS. 14A-14C depict a cartridge for performing a multiplexed assay. FIG. 14A shows a reagent strip for the cartridge. The oval holes are the supports for the detection modules, and these are constructed separately and then placed into the holes. The detection wells could be custom designed or commercially available. FIG. 14B shows the detection module for the cartridge depicted in FIG. 14A. In this example, the detection module contains two detection chambers, but could contain any number of chambers as required by the assay and as the detection system (the MR reader) is designed to accept. FIG. 14C depicts an alternate footprint for the modular multiplexed cartridge. This cartridge includes 3 detection modules that are molded as part of the reagent strip, and these portions are popped out of the frame and individually processed at other units (i.e., the NMR unit and/or magnetic assisted agglomeration (MAA) unit) within the assay system.

FIG. 15 is a scheme depicting one embodiment of the cycling gradient magnetic assisted agglomeration (gMAA) method of the invention. Two magnets are placed in two positions such that if the sample tube is placed close to the a region of strong magnetic field gradient produced by the first magnet, the magnetic particles will be drawn towards the direction of the field gradient produced by the first magnet, the sample tube is then placed next to the second magnet producing a field gradient, and the magnetic particles are drawn to the direction of the field gradient produced by second magnet. The cycle can be repeated until the aggregation reaction reaches a steady state (as observed by the change in the NMR relaxation rate of the sample); a smaller number of cycles can be used as well. A single magnet used to produce a field gradient can also be used, while for cycling the sample tube can be moved relative to the magnetic field gradient.

FIG. 16 is a scheme depicting a homogenous magnetic assisted agglomeration (hMAA) setup. On the left hand side, the magnetic particles are shown as dots in a partially clustered state. When exposed to a homogeneous magnetic field, as depicted on the right hand side, clustering of the magnetic particles is promoted as the magnetic particles form chains along the direction of the field produced by the hMAA setup. On the right hand side, the two magnets are represented by bars, to depict the formation of a standard dipole field. hMAA can also be used to evaluate the nonspecific reversibility of a magnetic particle to assess its utility in an assay of the invention.

FIG. 17 depicts a gradient MAA unit configured to apply a gradient magnetic field to the side and to the bottom of a sample. The specific setup has magnets with a surface field of approximately 0.7 T, while the produced gradient is in the order of 0.25 T/mm. Similar gMAA units, covering a much bigger range of fields and gradients can be used.

FIGS. 18A-18C depict a gradient MAA unit configured to apply a gradient magnetic field to the side and to the bottom of an array of samples. FIG. 18A depicts the gMAA unit array of 32 bottom magnets and 40 side magnets (32 functional, 8 used to balance the stray magnetic fields seen by all sample), each with a field strength of about 0.5 T, used for assisting agglomeration in an array of samples simultaneously. FIGS. 18B-18C depict a top view (FIG. 18B) and side view (FIG. 18C) of a setup for the automation of the an automated gMAA unit wherein a plate gMAA along with a configuration for containing an array of samples is cycled between the bottom and side magnet positions by a robotic systems, within a temperature controlled array. The magnets are stationary, while the plate holding the sample tubes moves through a preset trajectory. An exemplary field strength on the surface of individual magnets is 0.4-0.5 T, with a gradient in the order of 0.1 T/mm.

FIGS. 19A-19B depict a top view (FIG. 19A) and side view (FIG. 19B) of a homogenous MAA unit configured to apply a homogenous magnetic field to an array samples. Field strengths from 0.2-0.7 T can be used with homogeneity from 500 to 5000 ppm over the sample tube region.

FIG. 20 is a drawing of a vortexer which includes the following components: (i) a sample support, (ii) a main plate, (iii) four linkages, (iv) linear rail and carriage system (×2), (v) a support for driveshaft and rails, (vi) coupling and driveshaft, (vii) a mounting plate, and (viii) a drive motor.

FIG. 21 is a drawing of a compact vortexer which includes the following components: (i) a sample support, (ii) a main plate, (iii) two linkages, (iv) linear rail and carriage system, (v) a support for linear rail, (vi) support for driveshaft, (vii) coupling and driveshaft, (viii) a mounting plate, and (ix) a drive motor.

FIGS. 22A and 22B depict portions of a vortexer. FIG. 22A is a drawing depicting the bottom portion (i.e., the drive motor, coupling, and drive shaft) of a vortexer of the invention. The motor includes an index mark and/or other position sensing means such as an optical, magnetic or resistive position encoder that allows the motor to find a specific point in its rotation. These index marks are used to home the system, and ensure that the sample can be returned to a known position after mixing and allows the vortexer to be easily accessed by robotic actuators, and thus integrated into an automated system. In lieu of index marks, external home switches or position tracking sensors could be employed. FIG. 22B is a drawing depicting the guide mechanism of a vortexer of the invention. The main plate is connected to the offset axis of the drive shaft and is free to rotate. The plate follows the orbital path around and dictated by the motor shaft.

FIGS. 23A-23C are a series of drawings depicting a vortexer utilizing a planetary belt drive. FIG. 23A is an overall view showing the vortexer configured for one large tube. FIG. 23B is a section view showing two tube holders for small tubes. FIG. 23C is an overall view of vortexer showing four tubes and a close up of planetary belt drive mechanism.

FIG. 24 is a drawing depicting the components of the creatinine competitive assay of Example 6. A magnetic particle decorated with creatinine is used in combination with a creatinine antibody to form an aggregating system. The creatinine present in a liquid sample competes with the magnetic particles for the antibody, leading to a reduction in aggregation with increasing creatinine concentration. The change in aggregation is observed as a change in the T₂ relaxation rate of the hydrogen nuclei in the water molecules of the liquid sample. By comparing the observed T₂ relaxation rate of the liquid sample to a standard curve, the concentration of creatinine is determined.

FIGS. 25A-25C are a series of graphs showing the response curve for creatinine competitive assays. FIG. 25A is a graph showing a standard curve for the creatinine competitive assay of Example 6 correlating the observed T₂ relaxation rate with the concentration of creatinine in the liquid sample. FIG. 25B shows the T₂ response of a creatinine-decorated particle with 2 different preparations of antibody. Preparation 1 is pre-production (with aggregated antibody) and Preparation 2 is production purified (no aggregated antibody present). FIG. 25C shows the T₂ response of a creatinine-decorated particle with unaggregated antibody, biotinylated antibody and deliberately multimerized antibody, and confirms the increased clustering ability of multi-valent agglomerating agents.

FIG. 26 is a graph showing the specific clustering achieved, as determined via T₂ relaxation rates, with various methods of gMAA as described in Example 10. In FIG. 26 (i) “control” is gMAA (magnet exposure+vortex, repeat) in which the relative position of the sample and the magnetic field direction are unchanged with each cycle; (ii) “twist” is gMAA (magnet exposure+rotation within magnet, repeat) with rotating tube ca. 90° relative to the gradient magnet with each cycle; (iii) “180° turn” is gMAA (magnet exposure+remove tube from magnet, rotate, place back in magnet, repeat) with rotating tube ca. 180° relative to the gradient magnet with each cycle; and “remove 5 s” is removal of tube from magnet, 5 seconds rest (no rotation), repeat. The results show that the rate at which a steady state degree of agglomeration, and stable T₂ reading, is achieved is expedited by cycling between the two or more positions over a number of gMAA treatments. Further, field gradient combinations, cycling field (side or bottom) to null or side field to bottom, field (side or bottom) to vortex are also iterations that can be used for gMAA. Exposure or dwell times (either on the field or away), and number of cycles can be varied to optimize assisted aggregation for a specific assay (not shown).

FIG. 27 is a graph showing the response curve for the creatinine competitive assay for samples processed with alternating side-bottom magnet gMAA as described in Example 11.

FIG. 28 is a drawing depicting the tacrolimus competitive assay architecture of Example 9.

FIG. 29 is a graph showing a standard curve for the tacrolimus competitive assay of Example 9 correlating the observed T₂ relaxation rate observed for a liquid sample with the concentration of tacrolimus in the liquid sample.

FIGS. 30A-30B are graphs depicting the degree to which gMAA assisted aggregation is dependent upon temperature and dwell time in the assay of Example 11. FIG. 30A is a graph showing that the degree of aggregation as determined by measuring the T₂ response of the sample is increased with increasing dwell time at room temperature. FIG. 30B is a graph showing that the degree of aggregation as determined by measuring the T₂ response of the sample is increased with increasing gMAA dwell time at 37° C. As shown in FIGS. 30A and 30B, increasing temperature and increasing dwell time enhance the extent of gMAA assisted aggregation as observed by changes in the observed T₂.

FIG. 31 is a graph showing that the degree of aggregation as determined by measuring the T₂ response of the sample is increased with increasing the number of gMAA cycles in the assay of Example 13.

FIG. 32 is a drawing depicting the Candida agglomerative sandwich assay architecture of Example 14.

FIG. 33 is a graph depicting a creatinine inhibition curve (see Example 7) for using an antibody coated particle and an amino-dextran-creatinine multivalent binding agent to induce clustering by competing with any target analyte (creatinine) present in the sample to cause particle clustering. The binding agent used is a 40 kDa dextran with ˜10 creatinines per dextran molecule.

FIG. 34 is a graph depicting the evaluation of Tac-dextran conjugates for clustering ability (see Example 8) by performing a titration. As observed, that increased molecular weight of Tac-dextran results in the improved T₂ signal.

FIG. 35 is a graph depicting the evaluation of Tac-dextran conjugates for clustering ability (see Example 8) by performing a titration. As observed, higher substitution improved T₂ signal.

FIG. 36 is a graph depicting the evaluation of Tac-BSA conjugates for clustering ability (see Example 8) by performing a titration similar to that used for the Tac-dextran conjugates. As observed, clustering performance varies with the tacrolimus substitution ratio.

FIG. 37 is a graph depicting the results of T₂ assays for detecting anti-biotin antibody using prepared magnetic particles in blood and PBS matrices as described in Example 1.

FIG. 38 is a graph depicting results of T₂ assays for detecting anti-biotin antibody using prepared magnetic particles with (open circle) and without (filled circle) a protein block as described in Examples 8 and 9.

FIG. 39 is a graph depicting results of T₂ assays for detecting anti-biotin antibody using prepared magnetic particles having a BSA block (dark filled diamond, square, triangle) or an FSG block (light gray X's and circle) as described in Example 2.

FIGS. 40A-40B are schematics of provided particle coatings.

FIGS. 41A-41B depict results of T₂ assays for detecting biotin in a competitive assay format described in Example 4. FIG. 41A depicts experimental results in buffer; while FIG. 41B depicts experimental results in lysed blood.

FIG. 42 is a sketch of a system of the invention including an NMR unit, a robotic arm, a hMAA unit, a gMAA unit, two agitation units, a centrifuge, and a plurality of heating blocks.

FIGS. 43A-43D are images depicting various fluid transfer units which can be used in the systems of the invention.

FIGS. 44A and 44B are sketches showing how a system of the invention can be designed to regulate the temperature of the working space.

FIGS. 45A and 45B are sketches depicting an NMR unit having a separate casing for regulation of the temperature at the site of the NMR measurement, and useful where tight temperature control is needed for precision of the measurement. The temperature control configuration depicted in this figure is one of many different ways to control temperature.

FIG. 46A is a table and 46B is a graph depicting the repeatability of Candida measurements by methods of the invention over a period of eight days. To determine the repeatability of the T2 measurement on C. albicans infected human whole blood, we conducted an eight day study in which the same donor spiked and amplified sample was hybridized to the superparamagnetic particles (n=3) each day and the resulting T2 values were recorded (see Example 17). The within run precision is shown in FIG. 46A and in general is tight with the CV's of all measurands less than 12%. The repeatability observed over the course of eight days is shown in FIG. 46B (Mean T2 values+/−the 95% confidence intervals measured from the same donor spiked and amplified samples over the course of eight days) with the CVs less than 10% across the range of Candida concentrations and 6% for the negative control.

FIG. 47 is a scheme describing the work flow for detection of a bacterial or fungal pathogen in a whole blood sample (see Examples 14 and 17).

FIGS. 48A and 48B are graphs depicting results from donor samples. FIG. 48A is a graph depicting the results obtained from 16 experiments designed to assess the assay's performance in 6 different donor blood samples spiked with a range of C. albicans cells (see Example 17). Each data point is the mean+/−the 95% confidence interval (n=48). At the lowest test concentration (10 cells/mL), we failed to detect Candida albicans 37% of the time (6 out of 16 experiments); however at 100 cells/mL Candida albicans was detected 100% of the time. This suggests the assay can robustly detect at C. albicans concentrations greater than or equal to 100 cells/mL with no major inhibition of performance introduced through the donor blood samples. FIG. 48B is a graph depicting the results obtained from 7 experiments designed to assess the assay's performance in 6 different donor blood samples spiked with a range of C. krusei cells (see Example 17). Each data point is the mean+/− the 95% confidence interval (n=21). We do not detect at 10 cells/mL in any of the experimental runs but detect at 100 cells/mL for all experimental runs. This suggests the LOD between 10 and 100 cells/mL.

FIG. 49 is a dot diagram showing the T2 values measured for five C. albicans clinical isolates spiked into 400 μL whole blood at concentrations spanning 0 to 1E4 cells/mL. The plotted results are the mean+/− 1SD. The data indicates despite the scatter of absolute T2 values obtained among the different isolates, at 50 cells/mL all values are above that of the no Candida control (3 replicate measurements from 20 independent assays, total of 60 different clustering reactions).

FIGS. 50A and 50B are ROC plots of T2 results generated at 10 cells/mL (FIG. 50A) and 50 cells/mL (FIG. 50B). The area under the curve at 10 cells/mL is 0.72 (95 CI=0.56 to 0.88) while at 50 cells/mL the area under the curve is 0.98 (95 CI=0.95 to 1.001). The area under the curve is often used to quantify the diagnostic accuracy; in this case our ability to discriminate between a Candidemic patient with an infection of 10 cells/mL or 50 cells/mL versus a patient with no Candidemia. At 10 cells/mL the area under the curve is 0.72 which means that if the T2 assay was run on a randomly chosen person with Candidemia at a level of infection of 10 cells/mL, there is an 72% chance their T2 value would be higher than a person with no Candidemia. The clinical accuracy of the test is much higher at 50 cells/mL with the area under the curve at 0.98. Again indicating that in a person with Candidemia at this level of infection, the T2 assay would give a value higher than a sample from a patient without Candidemia 98% of the time. See Example 17.

FIG. 51 is a graph depicting the sensitivity of the assay using the standard thermocycle (˜3 hours turnaround time) and a process that combines the annealing/elongation steps (˜2 hours, 13 minutes turnaround time). Combining the annealing and elongation step in the thermocycling reduces the total assay TAT to 2.25 hours without compromising assay sensitivity.

FIG. 52 is a graph depicting the change in T₂ signal with PCR cycling (see Example 18). The results demonstrate that the methods and systems of the invention can be used to perform real time PCR and provide quantitative information about the amount of target nucleic acid present in a sample.

FIG. 53 is a series of photographs showing a simple magnetic separator/PCR block insert.

FIG. 54 is an image showing the quantity of DNA generated by amplification of (1) 100 copies of genomic C. albicans amplified in the presence of 3′ and 5′ C. albicans single probe nanoparticles; particles were held on the side wall during PCR via magnetic field, (2) 100 copies of genomic C. albicans amplified without nanoparticles, and (3) 100 copies of genomic C. albicans amplified in the presence of 3′ and 5′ C. albicans single probe nanoparticles; no magnetic field.

FIGS. 55A-55E are schematic views of a sample tube containing an immobilized portion of magnetizable metal foam (shaded), magnetic particles (circles), and analyte (triangles). a magnetizable metal foam, e.g., made of nickel, may be inserted into a conduit and immobilized by exposure to heat, which shrinks the conduit around the metal foam, resulting in a tight seal. A sample containing magnetic particles and analytes is then introduced at one end of the conduit (FIG. 55A). Next, the conduit is exposed to a magnet (FIG. 55B), and the magnetic particles are attracted to the metal foam and become magnetically trapped within its pores, or crevices. The average diameter of the pores in the metal foam is, e.g., between 100-1000 microns. Analyte molecules can be carried to the metal foam via binding to a magnetic particle, or the fluid can be forced through the metal foam to reach trapped magnetic particles. While trapped in the metal foam, the magnetic particles have enhanced interactions, as they are now confined and are closer to other magnetic particles, and cluster formation is enhanced. The metal foam is then demagnetized (FIG. 55C), i.e., the magnetic field of the metal foam becomes negligible. The magnetic particles and analyte cluster complexes largely remain in the metal foam, as the diffusion of magnetic particle clusters is relatively low, although some natural diffusion of the analyte in to and out of the metal foam occurs (FIG. 55D). Alternatively, the magnetizable metal foam (hollow cylinder) is free floating in the sample tube with the magnetic particles (circles), and analyte (stars). The magnetization and demagnetization of the free floating metal foam is used to increase the rate of aggregate formation.

FIG. 56A depicts a rotary gMAA configuration. The Rotary gMAA can include three configurations for varying magnetic field exposures—side-bottom; side-null and bottom-null (see Example 21).

FIG. 56B is a graph comparing T2 signal as a function of various rotary gMAA configurations for varying magnetic field exposures to a sample at a given agglomerator concentration. The rotary side-bottom configuration provided the highest T2 signal at a given agglomerator concentration, followed by the comparison side-bottom plate configuration. Rotary side-null provides equivalent signal to the plate side-bottom; and the bottom-null produces the lowest signal (see Example 21).

FIG. 57 is a table depicting the T2MR results for 32 clinical specimens indicates fourteen specimens are Candida positive. The test identifies four specimens containing C. krusei or C. glabrata, seven specimens containing C. albicans or C. tropicalis, and three containing C. parapsilosis. A solid black line indicates the decision threshold (T2=128 msec) (see Example 22).

DETAILED DESCRIPTION

The invention features systems, devices, and methods for the rapid detection of analytes or determination of analyte concentration in a sample. The systems and methods of the invention employ magnetic particles, an NMR unit, optionally one or more MAA units, optionally one or more incubation stations at different temperatures, optionally one or more vortexer, optionally one or more centrifuges, optionally a fluidic manipulation station, optionally a robotic system, and optionally one or more modular cartridges. The systems, devices, and methods of the invention can be used to assay a biological sample (e.g., blood, sweat, tears, urine, saliva, semen, serum, plasma, cerebrospinal fluid (CSF), feces, vaginal fluid or tissue, sputum, nasopharyngeal aspirate or swab, lacrimal fluid, mucous, or epithelial swab (buccal swab), tissues, organs, bones, teeth, or tumors, among others). Alternatively, the systems, devices, and methods of the invention are used to monitor an environmental condition (e.g., plant growth hormone, insecticides, man-made or environmental toxins, nucleic acid sequences that are important for insect resistance/susceptibility, algae and algae by-products), as part of a bioremediation program, for use in farming plants or animals, or to identify environmental hazards. Similarly, the systems, devices, and methods of the invention are used to detect and monitor biowarfare or biological warfare agents, such as ricin, Salmonella typhimurium, botulinum toxin, aflatoxin, mycotoxins, Francisella tularesis, small pox, anthrax, or others.

The magnetic particles can be coated with a binding moiety (i.e., antibody, oligo, etc.) such that in the presence of analyte, or multivalent binding agent, aggregates are formed. Aggregation depletes portions of the sample from the microscopic magnetic non-uniformities that disrupt the solvent's T₂ signal, leading to an increase in T₂ relaxation (see FIG. 3).

The T₂ measurement is a single measure of all spins in the ensemble, measurements lasting typically 1-10 seconds, which allows the solvent to travel hundreds of microns, a long distance relative to the microscopic non-uniformities in the liquid sample. Each solvent molecule samples a volume in the liquid sample and the T₂ signal is an average (net total signal) of all (nuclear spins) on solvent molecules in the sample; in other words, the T₂ measurement is a net measurement of the entire environment experienced by a solvent molecule, and is an average measurement of all microscopic non-uniformities in the sample.

The observed T₂ relaxation rate for the solvent molecules in the liquid sample is dominated by the magnetic particles, which in the presence of a magnetic field form high magnetic dipole moments. In the absence of magnetic particles, the observed T₂ relaxation rates for a liquid sample are typically long (i.e., T₂ (water)=˜2000 ms, T₂ (blood)=˜1500 ms). As particle concentration increases, the microscopic non-uniformities in the sample increase and the diffusion of solvent through these microscopic non-uniformities leads to an increase in spin decoherence and a decrease in the T₂ value. The observed T₂ value depends upon the particle concentration in a non-linear fashion, and on the relaxivity per particle parameter.

In the aggregation assays of the invention, the number of magnetic particles, and if present the number of agglomerant particles, remain constant during the assay. The spatial distribution of the particles change when the particles cluster. Aggregation changes the average “experience” of a solvent molecule because particle localization into clusters is promoted rather than more even particle distributions. At a high degree of aggregation, many solvent molecules do not experience microscopic non-uniformities created by magnetic particles and the T₂ approaches that of solvent. As the fraction of aggregated magnetic particles increases in a liquid sample, the observed T₂ is the average of the non-uniform suspension of aggregated and single (unaggregated) magnetic particles. The assays of the invention are designed to maximize the change in T₂ with aggregation to increase the sensitivity of the assay to the presence of analytes, and to differences in analyte concentration.

In designing magnetic relaxation switch (MRSw) biosensors, it is important to consider the relaxation mechanisms of the magnetic particles. First, in the case of superparamagnetic particles the solvent longitudinal and transverse relaxivities (defined as R₁=1/T₁ and R₂=1/T₂, respectively) are a function of particle size. Furthermore, R₂ and R₂* (where R₂*=1/T₂*, R₂*=R₂+Δω_(F), where Δω_(F) is dephasing due to field inhomgeneities) increase with particle diameter until about 100 nm, and then R₂ decreases with increasing particle size and the R₂* reaches a plateau for uniform fields (see FIG. 4A). Superparamagnetic particles are typically divided into categories of strongly magnetized and weakly magnetized particles, based on the relative magnitude of the precession frequency difference between nuclei at the surface of the particle and nuclei distant from the particle, Δω, and the inter-echo delay of the CPMG detection sequence, τ_(CP). Δω is essentially a relative measure of the effect of the dipolar magnetic field generated by a superparamagnetic particle on the resonant frequency of hydrogen nuclei in adjacent water molecules. When the product Δωτ_(CP)>1 then the particles are classified as strongly magnetized and when Δωτ_(CP)<1 then the particles are classified as weakly magnetized. For typical relaxometers, τ_(CP) is no shorter than tens of microseconds, so Δω must be less than 10⁵ for the particles to be within the weakly magnetized regime. Most superparamagnetic particles used for MRSw assays have a surface dephasing Δω of approximately 1×10⁷, therefore they are classified as strongly magnetized. This means that the inter-echo delay is always longer than the amount of dephasing that occurs at the surface of a particle.

Another characteristic of superparamagnetic particle solutions that is used to differentiate physical behavior is the diffusion time, or travel time, of water (τ_(D)) relative to the inter-echo time of the pulse sequence, τ_(CP). Particle solutions are in the long echo limit when the τ_(D) is significantly less than that τ_(CP). τ_(D) can be determined by the relationship:

$\begin{matrix} {{\tau_{D} = \frac{R^{2}}{D}},} & (1) \end{matrix}$ where τ_(D) is the time it takes a water molecule to diffuse the distance of a particle radius, R, and D the diffusion constant of water, 10⁻⁹ m²/s. τ_(D) can be thought of as the time it takes a water molecule to pass a hemisphere of a particle, or a flyby time. When τ_(D) is much larger than T_(CP), then the particle system is within the “short echo limit” Typical CPMG sequences have echo times on the order of hundreds of microseconds to several milliseconds. Therefore, the “short echo limit” cannot be approached unless the particle diameter approaches 1000 nm. The most common MRSw biosensors are within the “long echo limit” because the length of the inter-echo delays (τ_(CP)>0.25 ms) is longer than the time it takes a water molecule to diffuse past the hemisphere of a particle (0.2-100 microseconds).

As the particle size of a solution of superparamagnetic particles at fixed iron concentration is increased there is an initial increase in R₂, then a plateau and later decrease (FIG. 4A). The regime on the left hand side of the curve is been termed the motional averaging regime, the regime in the middle is been termed the static dephasing regime, and the regime on the right is been termed the visit limited, or slow motion regime. The boundaries between the motional averaging and visit limited regimes can be determined by generating plots such as that shown in FIG. 4A, or they can be determined by the relationship between Δω and τ_(D). If Δωτ_(D)<1, then the system is in the motional averaging regime; if Δωτ_(D)>1, then the system is in the visit limited regime (also termed the slow motion regime). As the diameter of the particles increases in the motional averaging regime the refocusing echos in the CPMG pulse sequence cannot efficiently refocus the magnetization that has been dephased by the particles, hence the increase in R₂ (or decrease in T₂). In other words, the refocusing pulses cannot compensate for increased dephasing by larger particles. The flat region of the static dephasing regime is due to the R₂ being limited by R₂*. The decreasing R₂ with increasing diameter in the visit limited regime results in the refocusing pulses being able to refocus the dephasing caused by the particles. Also apparent in FIG. 4A is that the R₂ in the slow motion regime exhibits a dependence on the inter-echo delay of the spin echo sequence.

In a homogenous magnetic field, one can determine which regime applies to a sample by comparing the R₂ to the R₂*; the two values are identical in the motional averaging or static dephasing regime and they are different in the visit limited regime. However, in cases of inhomogeneous fields, such as those present on benchtop and portable MR devices, the T₂* is dominated by the field gradient. In fact, the measured T₂* value is not indicative of the particle or particle cluster size state (FIG. 4B).

The shape of the R₂ response as particles agglomerated generally matches the expected trend for the increase in average particle size. The similarity between the R₂ of particle agglomerates and that of spherical particles suggests that one can equate particle aggregates and spherical shapes. Even though this assumption may seem to be in contradiction with the fractal nature of particle agglomerates, the shape of the particle aggregates observed by the magnetic resonance measurement is determined by the ensemble of diffusing water molecules in solution, which can be approximated by the radius of hydration measured by light scattering.

The analytical models for R₂ can be applied to magnetic relaxation biosensors to aid in the design of biosensor assays. Conveniently, these models accurately predict the dependence of R₂ on parameters that a biosensor designer can control—iron concentration, temperature, magnetic susceptibility, and particle size. Additionally, these analytical models allow for predictive modeling of the dependence of T₂ relaxation on these parameters. Results are not entirely quantitative, but the general trends and response curves predicted by these models can be instructive. One useful model is the chemical exchange model for strongly magnetized spheres:

$\begin{matrix} {{1/T_{2}} = \frac{\left( {4/9} \right)V\;{\tau_{D}\left( {\Delta\;\omega_{r}} \right)}^{2}}{1 + {\left( {4/9} \right)^{2}\left( {\tau_{D}/\tau_{CP}} \right)^{2}\alpha^{5}}}} & (2) \\ {\alpha = \left\lbrack \frac{\Delta\;\omega\;\tau_{CP}}{a + {b\;\Delta\;\omega\;\tau_{CP}V}} \right\rbrack^{1/3}} & (3) \end{matrix}$ where 1/T₂ is the transverse relaxivity, V the volume fraction of iron in solution, Δ_(D) the diffusion, or flyby time, Δω_(r) the frequency shift at the surface of a particle relative to bulk solution, τ_(CP) one half the inter-echo delay in a CPMG sequence, and a and b are derived constants (a=1.34 and b=0.99). Equations (2) and (3) can be used to generate a curve that describes the dependence of R₂ on particle sizes, as shown by the light and dark lines in FIGS. 4A and 4B (dark line on right side of the curve; light line on left side of the curve).

A modification of Equation 2 can be used to generate a plot that is more intuitive to an assay developer. This plot is in terms of T₂ and particle diameter with linear units rather than logarithmic units (FIG. 2). As discussed above, magnetic relaxation biosensor assays function due to a transition between dispersed and clustered states. For a given agglomerative assay, the measured T₂ can follow one of two pathways over the course of an analyte titration. The population of dispersed particles can cluster in a uniform manner leading to an increase in average particle size that is proportional to the amount of analyte that has been added. This type of agglomeration is termed the monodisperse model because it would lead to a monodisperse intermediate population of particles. In this case, T₂ would be expected to decrease as particle size increases as long as the system is within the motional averaging regime. As the system approaches and enters the visit limited regime the T₂ would increase with particle size (FIG. 4C).

A different type of agglomeration that may occur is one in which the addition of analyte seeds the self-assembly of clusters, a process with energetics similar to crystal formation or fractal aggregation. For this model one would expect a preferred size for particle clusters that depended on the conditions of the solution. Systems that followed this model would exhibit polydisperse intermediate populations; one would find a mixture of particles with discrete sizes. Given two discrete populations, dispersed particles and clustered particles, the system would transition between the T₂ value of the starting monodisperse population of unclustered particles and the final T₂ value of the fully clustered particles. For both models, full titration may lead to a monodisperse solution of clustered particles. Although the exact energetics, kinetics, and thermodynamics of particle agglomeration will depend on characteristics of the assay system such as valency and binding affinities, these two models are instructive in understanding the dependencies and possible scenarios one may encounter during MRSw biosensor design.

There are two regimes for particle clustering and T₂ affects based on particle size (see FIG. 4D, the boundary is typically ca. 100 nm diameter particles). For any given assay of a liquid sample the particle count for 250 nm sized magnetic particles can be ca. 1×10⁷ particles, whereas for 30 nm sized magnetic particles can be ca. 1×10¹³. This is because the smaller particles have a lower relaxivity per particle (for the same type of material), resulting in an inherent sensitivity disadvantage. In a typical assay of the invention, the magnetic particles are selected such that T₂ increases with an increase in the fraction of aggregated particles.

The assay of the invention can be designed to change the direction of T₂ in the presence of analyte (see FIGS. 5A-5C). For example, the assay can be an agglomerative sandwich immunoassay in which two populations of magnetic particles bind to different epitopes of an analyte (see FIG. 5A); a competitive assay in which analyte competes with a multivalent binding agents to inhibit the aggregation of magnetic particles (see FIG. 5B); or a hybridization-mediated agglomeration in which two populations of magnetic particles bind to a first and second portion of an oligonucleotide (see FIG. 5C). Additional competitive format might include when two particles binding moieties bind without agglomerator (e.g., the DNA oligonucleotides are designed so that two nanoparticles have two different oligos and they can anneal together and when heated the analyte or amplicon or target DNA competes or disrupts the np annealing).

Other formats for carrying out the assays of the invention can be used, such as: (i) a target sample can be incubated in the presence of a magnetic particle that has been decorated with binding moieties specific to a target analyte and a multivalent binding agent, in an inhibition assay the binding of the analyte to the magnetic particles blocks agglomeration of the magnetic particles with the multivalent binding agent; (ii) a target sample can be incubated in the presence of a magnetic particle that has been decorated with binding moieties specific to a target analyte and a multivalent binding agent, in a disaggregation assay the analyte is exposed to a pre-formed aggregate of the multivalent binding agent and the magnetic particle and the analyte displaces the multivalent binding agent to reduce aggregation in the liquid sample; or (iii) a target sample can be incubated in the presence of a magnetic particle that has been decorated with binding moieties specific to a target analyte and the target analyte itself to form a self-assembling single population of magnetic particles, in an inhibition assay or disaggregation assay the presence the binding of the analyte to the magnetic particles blocks the self agglomeration of the magnetic particles; or (iv) a target sample can be incubated in the presence of a soluble agglomerating agent and a magnetic particle decorated with the analyte or analog of the analyte, in an inhibition assay the presence of the analyte binds the soluble agglomerating agent blocking the agglomeration of the particles.

Where a multivalent binding agent (agglomerant) is employed, multiple analytes are linked to a carrier (e.g., a simple synthetic scaffold, or a larger carrier protein or polysaccharide, such as BSA, transferrin, or dextran).

Assay Reagents

The surfactant may be selected from a wide variety of soluble non-ionic surface active agents including surfactants that are generally commercially available under the IGEPAL trade name from GAF Company. The IGEPAL liquid non-ionic surfactants are polyethylene glycol p-isooctylphenyl ether compounds and are available in various molecular weight designations, for example, IGEPAL CA720, IGEPAL CA630, and IGEPAL CA890. Other suitable non-ionic surfactants include those available under the trade name TETRONIC 909 from BASF Wyandotte Corporation. This material is a tetra-functional block copolymer surfactant terminating in primary hydroxyl groups. Suitable non-ionic surfactants are also available under the VISTA ALPHONIC trade name from Vista Chemical Company and such materials are ethoxylates that are non-ionic biodegradables derived from linear primary alcohol blends of various molecular weights. The surfactant may also be selected from poloxamers, such as polyoxyethylene-polyoxypropylene block copolymers, such as those available under the trade names Synperonic PE series (ICI), Pluronic® series (BASF), Supronic, Monolan, Pluracare, and Plurodac, polysorbate surfactants, such as Tween® 20 (PEG-20 sorbitan monolaurate), and glycols such as ethylene glycol and propylene glycol.

Such non-ionic surfactants may be selected to provide an appropriate amount of detergency for an assay without having a deleterious effect on assay reactions. In particular, surfactants may be included in a reaction mixture for the purpose of suppressing non-specific interactions among various ingredients of the aggregation assays of the invention. The non-ionic surfactants are typically added to the liquid sample prior in an amount from 0.01% (w/w) to 5% (w/w).

The non-ionic surfactants may be used in combination with one or more proteins (e.g., albumin, fish skin gelatin, lysozyme, or transferrin) also added to the liquid sample prior in an amount from 0.01% (w/w) to 5% (w/w).

Furthermore, the assays, methods, and cartridge units of the invention can include additional suitable buffer components (e.g., Tris base, selected to provide a pH of about 7.8 to 8.2 in the reaction milieu); and chelating agents to scavenge cations (e.g., EDTA disodium, ethylene diamine tetraacetic acid (EDTA), citric acid, tartaric acid, glucuronic acid, saccharic acid or suitable salts thereof).

Analytes

Embodiments of the invention include devices, systems, and/or methods for detecting and/or measuring the concentration of one or more analytes in a sample (e.g., a protein, a peptide, an enzyme, a polypeptide, an amino acid, a nucleic acid, an oligonucleotide, a therapeutic agent, a metabolite of a therapeutic agent, RNA, DNA, circulating DNA (e.g., from a cell, tumor, pathogen, or fetus), an antibody, an organism, a virus, bacteria, a carbohydrate, a polysaccharide, glucose, a lipid, a gas (e.g., oxygen and/or carbon dioxide), an electrolyte (e.g., sodium, potassium, chloride, bicarbonate, BUN, magnesium, phosphate, calcium, ammonia, and/or lactate), general chemistry molecules (creatinine, glucose), a lipoprotein, cholesterol, a fatty acid, a glycoprotein, a proteoglycan, and/or a lipopolysaccharide). The analytes may include identification of cells or specific cell types. The analyte(s) may include one or more biologically active substances and/or metabolite(s), marker(s), and/or other indicator(s) of biologically active substances. A biologically active substance may be described as a single entity or a combination of entities. The term “biologically active substance” includes without limitation, medications; vitamins; mineral supplements; substances used for the treatment, prevention, diagnosis, cure or mitigation of disease or illness; or substances which affect the structure or function of the body; or pro-drugs, which become biologically active or more active after they have been placed in a predetermined physiological environment; or biologically toxic agents such as those used in biowarfare including organisms such as anthrax, ebola, Salmonella typhimurium, Marburg virus, plague, cholera, Francisella tulariesis (tularemia), brucellosis, Q fever, Bolivian hemorrhagic fever, Coccidioides mycosis, glanders, Melioidosis, Shigella, Rocky Mountain spotted fever, typhus, Psittacosis, yellow fever, Japanese B encephalitis, Rift Valley fever, and smallpox; naturally-occurring toxins that can be used as weapons include ricin, aflatoxin, SEB, botulinum toxin, saxitoxin, and many mycotoxins. Analytes may also include organisms such as Candida albicans, Candida glabrata, Candida krusei, Candida parapsilosis, Candida tropicalis, Coagulase negative Staphalococcus, Enterococcus faecalis, Enterococcus faecium, Escherichia coli, Klebsiella pneumonia, Pseudomonas aeruginosa, Staphylococcus aureus, Acinetobacter baumannii, Aspergillus fumigates, Bacteroides fragilis, Bacteroides fragilis, blaSHV, Burkholderia cepacia, Campylobacter jejuni/coli, Candida guilliermondii, Candida lusitaniae, Clostridium pefringens, Enterobacter aeraogenesl, Enterobacter cloacae, Enterobacteriaceae spp., Haemophilus influenza, Kingella kingae, Klebsiella oxytoca, Listeria monocytogenes, Mec A gene-bearing bacteria (MRSA), Morganella morgana, Neisseria meningitides, Neisseria spp., non-meningitidis, Prevotella buccae, Prevotella intermedia, Prevotella melaminogenica, Propionibacterium acnes, Proteus mirabilis, Proteus vulgaris, Salmonella enteric, Serratia marcescens, Staphylococcus haemolyticus, Staphylococcus maltophilia, Staphylococcus saprophyticus, Stenotrophomonas maltophilia, Stenotrophomonas maltophilia, Streptococcus agalactie, Streptococcus bovis, Streptococcus dysgalactie, Streptococcus mitis, Streptococcus mutans, Streptococcus pneumonia, Streptococcus pyogenes, Streptococcus sanguinis, Van A gene, Van B gene. Analytes may also include viral organisms such as dsDNA viruses (e.g., adenoviruses, herpes viruses, poxviruses); ssDNA viruses (+)sense DNA (e.g., parvoviruses); dsRNA viruses (e.g., reoviruses); (+)ssRNA viruses (+)sense RNA (e.g., picornaviruses, togaviruses); (−)ssRNA viruses (−)sense RNA (e.g., orthomyxoviruses, rhabdoviruses); ssRNA-RT viruses (+)sense RNA with DNA intermediate in life-cycle (e.g., retroviruses); and dsDNA-RT viruses (e.g., hepadnaviruses).

Opportunistic infections which can be detected using the systems and methods of the invention include, without limitation, fungal, viral, bacterial, protozoan infections, such as: 1) fungal infections, such as those by Candida spp. (drug resistant and non-resistant strains), C. albicans, C. krusei, C. glabrata, and Aspergillus fumigates; 2) gram negative infections, such as those by E. coli, Stenotrophomonas maltophilia, Klebsiella pneumonia/oxytoca, and Pseudomonas aeruginosa; and 3) gram positive infections, such as those by Staphylococcus spp., S. aureus, S. pneumonia, Enterococcus ssp. (E. faecalis and E. faecium). The infection can be by coagulase negative staphylococcus, Corynebacterium spp., Fusobacterium spp., Morganella morganii, Pneumocystis jirovecii (previously known as Pneumocystis carinii), F. hominis, S. pyogenes, Pseudomonas aeruginosa, polyomavirus JC polyomavirus (the virus that causes progressive multifocal leukoencephalopathy), Acinetobacter baumanni, Toxoplasma gondii, cytomegalovirus, Aspergillus spp., Kaposi's Sarcoma, Cryptosporidium spp., Cryptococcus neoformans, and Histoplasma capsulatum.

Medical Conditions

The systems and methods of the invention can also be used to monitor and diagnose infectious disease in a multiplexed, automated, no sample preparation system. Examples of pathogens that may be detected using the devices, systems, and methods of the invention include, e.g., Candida (resistant and non-resistant strains), e.g., C. albicans, C. glabrata, C. krusei, C. tropicalis, and C. parapsilosis; A. fumigatus; E. coli, Stenotrophomonas maltophilia, Klebsiella pneumonia/oxytoca, P. aeruginosa; Staphylococcus spp. (e.g., S. aureus or S. pneumonia); E. faecalis, E. faecium, Coaglulase negative staphylococcus spp., Corynebacterium spp., Fusobacterium spp., Morganella morganii, Pneumocystis jirovecii, previously known as pneumocystis carinii, F. hominis, streptococcus pyogenes, Pseudomonas aeruginosa, Polyomavirus JC polyomavirus (the virus that causes progressive multifocal leukoencephalopathy), Acinetobacter baumanni, Toxoplasma gondii, Cytomegalovirus, Aspergillus spp., Kaposi's Sarcoma, cryptosporidium, Cryptococcus neoformans, and Histoplasma capsulatum, among other bacteria, yeast, fungal, virus, prion, mold, actinomycetes, protozoal, parasitic, protist and helminthic infectious organisms.

The systems and methods of the invention can be used to identify and monitor the pathogenesis of disease in a subject, to select therapeutic interventions, and to monitor the effectiveness of the selected treatment. For example, for a patient having or at risk of a viral infection, the systems and methods of the invention can be used to identify the infectious virus, viral load, and to monitor white cell count and/or biomarkers indicative of the status of the infection. The identity of the virus can be used to select an appropriate therapy. The therapeutic intervention (e.g., a particular antiviral agent) can be monitored as well to correlate the treatment regimen to the circulating concentration of antiviral agent and viral load to ensure that the patient is responding to treatment.

The systems and methods of the invention can be used to monitor a viral infection in a subject, e.g., with a viral panel configured to detect Cytomegalovirus (CMV), Epstein Barr Virus, BK Virus, Hepatitis B virus, Hepatitis C virus, Herpes simplex virus (HSV), HSV1, HSV2, Respiratory syncytial virus (RSV), Influenza; Influenza A, Influenza A subtype H1, Influenza A subtype H3, Influenza B, Human Herpes Virus 6, Human Herpes Virus 8, Human Metapneumovirus (hMPV), Rhinovirus, Parainfluenza 1, Parainfluenza 2, Parainfluenza 3, and Adenovirus. The methods of the invention can be used to monitor a suitable therapy for the subject with a viral infection (e.g., Abacavir, Aciclovir, Acyclovir, Adefovir, Amantadine, Amprenavir, Ampligen, Arbidol, Atazanavir, Atripla, Boceprevir, Cidofovir, Combivir, Darunavir, Delavirdine, Didanosine, Docosanol, Edoxudine, Efavirenz, Emtricitabine, Enfuvirtide, Entecavir, Famciclovir, Fomivirsen, Fos amprenavir, Foscarnet, Fosfonet, Ganciclovir, Ibacitabine, Immunovir, Idoxuridine, Imiquimod, Indinavir, Inosine, Integrase inhibitor, Interferon type III, Interferon type II, Interferon type I, Interferon α, Interferon β, Lamivudine, Lopinavir, Loviride, Maraviroc, Moroxydine, Methisazone, Nelfinavir, Nevirapine, Nexavir, Nucleoside analogues, Oseltamivir (Tamiflu), Peginterferon alfa-2a, Penciclovir, Peramivir, Pleconaril, Podophyllotoxin, Raltegravir, Reverse transcriptase inhibitor, Ribavirin, Rimantadine, Ritonavir, Pyramidine, Saquinavir, Stavudine, Tea tree oil, Tenofovir, Tenofovir disoproxil, Tipranavir, Trifluridine, Trizivir, Tromantadine, Truvada, Valaciclovir (Valtrex), Valganciclovir, Vicriviroc, Vidarabine, Viramidine, Zalcitabine, Zanamivir (Relenza), or Zidovudine), and to monitor the circulating concentration of the therapeutic administered to the subject.

The systems and methods of the invention can also be used to monitor HIV/AIDS patients. When clinicians suspect acute infection (e.g., in a subject with a report of recent risk behavior in association with symptoms and signs of the acute retroviral syndrome), a test for HIV RNA is usually performed. High levels of HIV RNA detected in plasma through use of sensitive amplification assays (PCR, bDNA, or NASBA), in combination with a negative or indeterminate HIV antibody test, support the diagnosis of acute HIV infection. Low-level positive PCR results (<5000 copies/mL) are often not diagnostic of acute HIV infection and should be repeated to exclude a false-positive result. HIV RNA levels tend to be very high in acute infection; however, a low value may represent any point on the upward or downward slope of the viremia associated with acute infection. Plasma HIV RNA levels during seroconversion do not appear significantly different in subjects who have acute symptoms versus those who are asymptomatic. Viremia occurs approximately 2 weeks prior to the detection of a specific immune response. Subjects diagnosed with acute HIV infection by HIV RNA. Fever and flu- or mono-like symptoms are common in acute HIV infection but are nonspecific rash, mucocutaneous ulcers, or pharyngeal candidiasis and meningismus are more specific and should raise the index of suspicion testing still require antibody testing with confirmatory Western blot 3 to 6 weeks later.

Subjects undergoing HIV testing who are not suspected to be in the acute stages of infection should receive HIV antibody testing according to standard protocol. Antibody test results that are initially negative should be followed up with HIV antibody testing at 3 months to identify HIV infection in individuals who may not yet have seroconverted at the time of initial presentation. Plasma HIV RNA levels indicate the magnitude of HIV replication and its associated rate of CD4+ T cell destruction, while CD4+ T-cell counts indicate the extent of HIV-induced immune damage already suffered. Regular, periodic measurement of plasma HIV RNA levels and CD4+ T-cell counts is necessary to determine the risk of disease progression in an HIV-infected individual and to determine when to initiate or modify antiretroviral treatment regimens.

As rates of disease progression differ among individuals, treatment decisions should be individualized by level of risk indicated by plasma HIV RNA levels and CD4+ T-cell counts. Current WHO guidelines and recommendations for HIV therapy includes a combination of the following drugs, AZT (zidovudine), 3TC (lamivudine), ABC (abacavir), ATV (atazanavir), d4T (stavudine), ddI (didanosine), NVP (nevirapine), EFV (efavirenz), FTC (emtricitabine), LPV (lopinavir), RTV (ritonavir), TDF (tenofovir disoproxil fumarate) in established regimens. Drug therapy for HIV is to commence in subjects who have a CD4 count <350 cell/mm³ irrespective of clinical symptoms. At least one of the four following regimens for antiretroviral naïve subjects is begun: 1) AZT+3TC+EFV, 2) AZT+3TC+NVP, 3) TDF+3TC or FTC+EFV, or 4) TDF+3TC or FTC+NVP. These regimens avoid d4T (stavudine) to limit the disfiguring, unpleasant, and potentially life-threatening toxicities of this drug. Treatment failure is usually determined by viral load, a persistent value of 5,000 copies/ml confirms treatment failure. In cases whereby viral load measurement is not available, immunological criteria (CD4 cell count) can be used to determine therapeutic progress. In cases of treatment failure, a boosted protease inhibitor plus two nucleoside analogs are added to the regimen and is considered second line antiretroviral therapy. ATV plus low dose RTV, or LPV with low dose RTV is also considered second line therapy. Often the goal in treatment failure cases is simpler timed regimens and fixed doses.

For subjects failing the second line treatment regimens should be maintained on a tolerated regimen for the duration. The use of potent combination antiretroviral therapy to suppress HIV replication to below the levels of detection of sensitive plasma HIV RNA assays limits the potential for selection of antiretroviral-resistant HIV variants, the major factor limiting the ability of antiretroviral drugs to inhibit virus replication and delay disease progression. Therefore, maximum achievable suppression of HIV replication should be the goal of therapy. The most effective means to accomplish durable suppression of HIV replication is the simultaneous initiation of combinations of effective anti-HIV drugs with which the subject has not been previously treated and that are not cross-resistant with antiretroviral agents with which the subject has been treated previously. Each of the antiretroviral drugs used in combination therapy regimens should always be used according to optimum schedules and dosages. The available effective antiretroviral drugs are limited in number and mechanism of action, and cross-resistance between specific drugs has been documented. Therefore, any change in antiretroviral therapy increases future therapeutic constraints.

Monitoring HIV/AIDS subjects for viral load, drug levels, CD4 cell counts, and toxicity patterns in a single platform diagnostic method would provide distinct advantages to a subject. The systems and methods of the invention can be used in a multiplexed, no sample preparation, single detection method, automated system to determine the drug level, the toxicity or adverse effect determinants, and the potential biomarker of the progression of the disease. For example, a cartridge having portals or wells containing 1) magnetic particles having CD4 cell specific antibodies decorated on their surface, 2) magnetic particles having toxicity biomarker specific antibodies on their surface, and 3) magnetic particles having nucleic acid specific probes to identify viral load levels could be employed to rapidly determine and provide clinical management values for a given HIV/AIDS subject.

The systems and methods of the invention can also be used to monitor and diagnose infectious disease and inflammation in a multiplexed, automated, no sample preparation system. Such systems and methods could be used to monitor, for example, bacteremia, sepsis, and/or Systemic Inflammatory Response Syndrome (SIRS). Early diagnosis is clinically important as this type of infection, if left untreated, can lead to organ dysfunction, hypoperfusion, hypotension, refractory (septic) shock/SIRS shock, and/or Multiple Organ Dysfunction Syndrome (MODS). For a typical patient, many bacterial or fungal infections are the result of incubation at the time of admission to a healthcare setting and are termed healthcare-associated infections (HAI), also known as nosocomial, hospital-acquired or hospital-onset infections. Healthcare-associated infections are most commonly caused by viral, bacterial, and fungal pathogens and are commonly transmitted via wounds, invasive devices (catheters, tracheostomy, intubation, surgical drains) or ventilators and are found as urinary tract infections, surgical site infections, or a form of pneumonia. Within hours after admission, a patient's flora begins to acquire characteristics of the surrounding bacterial pool. Most infections that become clinically evident after 48 hours of hospitalization are considered hospital-acquired and the pathogens should be investigated in all febrile patients who are admitted for a nonfebrile illness or those who develop clinical deterioration unexplained by the initial diagnosis. More careful and selective use of antimicrobial agents, such as antibiotics, is also desirable to decrease the selection pressure for the emergence of resistant strains. Infections that occur after the patient is discharged from the hospital can be considered healthcare-associated if the organisms were acquired during the hospital stay. Patient-related risk factors for invasion of colonizing pathogen include severity of illness, underlying immunocompromised state and/or the length of in-patient stay. Risk factors for the development of catheter-associated bloodstream infections in neonates include catheter hub colonization, exit site colonization, catheter insertion after the first week of life, duration of parenteral nutrition, and extremely low birth weight (<1000 g) at the time of catheter insertion. In patients in the PICU risks, for catheter-associated bloodstream infections increase with neutropenia, prolonged catheter dwell time (>7 days), use of percutaneously placed CVL (higher than tunneled or implanted devices), and frequent manipulation of lines. Candida infections are increasingly important pathogens in the NICU. Risk factors for the development of candidemia in neonates include gestational age less than 32 weeks, 5-min Apgar scores of less than 5, shock, disseminated intravascular coagulopathy, prior use of intralipids, parenteral nutrition administration, CVL use, H2 blocker administration, intubation, or length of stay longer than 7 days. Risk factors for the development of ventilator-associated pneumonia (VAP) in pediatric patients include reintubation, genetic syndromes, immunodeficiency, and immunosuppression. In neonates, a prior episode of bloodstream infection is a risk factor for the development of VAP. Risk factors for the development of healthcare-associated urinary tract infection in pediatric patients include bladder catheterization, prior antibiotic therapy, and cerebral palsy. Among the categories of bacteria most known to infect immunocompromised patients are MRSA (Methicillin resistant Staphylococcus aureus), gram-positive bacteria and Helicobacter, which is gram-negative. While there are antibiotic drugs that can treat diseases caused by Gram-positive MRSA, there are currently few effective drugs for Acinetobacter. Common pathogens in bloodstream infections are coagulase-negative staphylococci, Enterococcus, and Staphylococcus aureus. In addition, Candida albicans and pathogens for pneumonia such as Pseudomonas aeruginosa, Staphylococcus aureus, Klebsiella pneumoniae, and Haemophilus influenza account for many infections. Pathogens for urinary tract infections include Escherichia coli, Candida albicans, and Pseudomonas aeruginosa. Gram-negative enteric organisms are additionally common in urinary tract infections. Surgical site infections include Staphylococcus aureus, Pseudomonas aeruginosa, and coagulase-negative staphylococci. The infectious agent can be selected from, without limitation, pathogens associated with sepsis, such as Acinetobacter baumannii, Aspergillus fumigatis, Bacteroides fragilis, B. fragilis, blaSHV, Burkholderia cepacia, Campylobacter jejuni/coli, Candida guilliermondii, C. albicans, C. glabrata, C. krusei, C. Lusitaniae, C. parapsilosis, C. tropicalis, Clostridium pefringens, Coagulase negative Staph, Enterobacter aeraogenes, E. cloacae, Enterobacteriaceae, Enterococcus faecalis, E. faecium, Escherichia coli, Haemophilus influenzae, Kingella Kingae, Klebsiella oxytoca, K. pneumoniae, Listeria monocytogenes, Mec A gene (MRSA), Morganella morgana, Neisseria meningitidis, Neisseria spp. non-meningitidis, Prevotella buccae, P. intermedia, P. melaminogenica, Propionibacterium acnes, Proteus mirabilis, P. vulgaris, Pseudomonas aeruginosa, Salmonella enterica, Serratia marcescens, Staphylococcus aureus, S. haemolyticus, S. maltophilia, S. saprophyticus, Stenotrophomonas maltophilia, S. maltophilia, Streptococcus agalactie, S. bovis, S. dysgalactie, S. mitis, S. mutans, S. pneumoniae, S. pyogenes, and S. sanguinis; or any other infectious agent described herein. In certain instances, the method and system will be designed to ascertain whether the infectious agent bears a Van A gene or Van B gene characteristic of vancomycin resistance; mecA for methicillin resistance, NDM-1 and ESBLfor more general resistance to beta-lactams.

To determine whether a patient has sepsis, it is necessary to identify the presence of a pathogen. To most effectively treat a patient, the earliest initiation of appropriate therapy is critical. Antimicrobial and other treatments for sepsis rely on the classification of pathogens at multiple levels, including the identification of an agent as 1) bacterial, viral, fungal, parasitic or otherwise; 2) gram positive, gram negative, yeast, or mold, 3) species, and 4) susceptibility.

Each of these levels of specificity improves the time to initiation of appropriate therapy, and each step further down the track will lead to a narrowing of therapeutic agents to the most specific set. Without absolute susceptibility data, empiric approaches to care rely on the information available about the pathogen (at whichever level) and the pattern of pathogen frequency and susceptibility trends in the hospital of another site of care. Thus, certain categories of pathogens are frequently presumed to be causative until there are more data to refine the pairing of pathogen and therapy. Specifically, these targets fall into the ESKAPE category (which is a series of resistant pathogens) and the SPACE category, which is a set of high virulence pathogens that require isolation of patients.

In addition to identifying these pathogens in multiple sample types (blood, tissue, urine, etc.), another method to distinguish symptomatic patients, for instance, patients with systemic inflammatory syndrome, or SIRS, from septic patients, is to use biomarkers that correlate either individually or via an index, to identify patients with infection. In cases where infections are not detected due to antimicrobial therapy interference with diagnostics, immune system control of the therapy, or otherwise, these biomarkers, which can be multiple types of analytes (cytokines, metabolites, DNA, RNA/gene expression, etc.) will indicate infection and thus sepsis.

To generate the diagnostic information required for both the presence of an infection and some level of species identification, one panel could be: (i) gram positive clusters (e.g., S. aureus, and CoNS (coagulase negative staph)); (ii) gram positive chains/pairs (e.g., Strep spp., mitis, pneumonia spp., agalactiae spp., pyogenes spp., Enterococcus spp. (E. faecium, E. fecalis); (iii) gram negative rods (e.g., E. coli, Proteus spp., Klebsiella spp., Serratia spp., Acinetobacter spp., Stenotrophomonas spp.); (iv) SPACE (e.g., Serratia spp., Pseudomonas spp., Acinetobacter spp., Citrobacter spp., Enterobacter spp.); (v) Pseudomonas (e.g., Pseudomonas spp.); (vi) ESKAPE (E. faecium, Staphylococcus aureas, Klebsiella spp., Acinetobacter spp., Pseudomonas spp., Enterobacter spp.); and (vii) Pan-Bacterial (all bacterial species).

This panel should be used in conjunction with a fungal assay for full coverage. The categories represent the information required for an effective intervention with appropriate therapy, given that each site of care will have an empirically derived approach based on a positive response to gram +, gram −, etc. The species identified in each category represent those that would fit under each heading, but are not comprehensive. Further, a pan-bacterial marker is included to cover any species that is not covered by the diagnostic method employed for each category. Further, the combination of results will also give an indication of the species, although not fully, if included as described above. Cross-referencing positives and negatives by category allow a process of elimination approach to identify some of the species, probabilistically.

In addition to pathogen panels, a standalone or companion test could be performed for biomarkers that can indicate sepsis. Examples of these markers are below, and may be used individually or in combination: IL-1β, GRO-alpha, High mobility group-box 1 protein (HMGB-1), IL-1 receptor, IL-1 receptor antagonist, IL-1b, IL-2, IL-4, IL-6, IL-8, IL-10, IL-12, IL-13, IL-18, macrophage inflammatory protein (MIP-1), macrophage migration inhibitory factor (MIF), osteopontin, RANTES (regulated on activation, normal T-cell expressed and secreted; or CCL5), IL-10, GM-CSF, MCP-1, TNF-α, hsCRP, PCT, LFB, and lactate.

Amplification and Detection of Nucleic Acids from Complex Samples

Systems and methods of the invention can include amplification based nucleic acid detection assays conducted starting with complex samples (e.g., for diagnostic, forensic, and environmental analyses).

Sample preparation must also remove or provide resistance for common PCR inhibitors found in complex samples (e.g., body fluids, soil, or other complex milieu). Common inhibitors are listed in Table 1 (see also, Wilson, Appl. Environ. Microbiol., 63:3741 (1997)). Inhibitors typically act by either prevention of cell lysis, degradation or sequestering a target nucleic acid, and/or inhibition of a polymerase activity. The most commonly employed polymerase, Taq, is inhibited by the presence of 0.1% blood in a reaction. Very recently, mutant Taq polymerases have been engineered that are resistant to common inhibitors (e.g., hemoglobin and/or humic acid) found in blood and soil (Kermekchiev et al., Nucl. Acid. Res., 37(5): e40, (2009)). Manufacturer recommendations indicate these mutations enable direct amplification from up to 20% blood. Despite resistance afforded by the mutations, accurate real time PCR detection is complicated due to fluorescence quenching observed in the presence of blood sample (Kermekchiev et al., Nucl. Acid. Res., 37:e40 (2009)).

TABLE 1 PCR inhibitors and facilitators/methods for overcoming inhibition. Substrate Target Inhibitor Facilitator feces Escherichia >10{circumflex over ( )}3 bacterial cells ion-exchange column coli CSF Treponema Cellular debris causing nested primers pallidum nonspecific amplification whole blood mammalian >4 μl of blood/100-ml reaction 1-2% blood per reaction tissue mix (hemoglobin) feces Rotatvirus unknown dilution cellulose fiber clinical Cytomegalovirus unidentified components glass bead extraction specimens human blood human genes DNA binding proteins thermophilic protease and tissue from Thermus strain rt44A mammalian Mammalian thermal cycler variations formamide tissue tissue genetics mammalian Mammalian thermal cycler variations DMSO, glycerol, PEG, tissue tissue genetics organic solvents clinical Treponema unknown factors Various substrate- specimens pallidum specific physicochemical methods forensic Sperm Genotyping errors; semen selective/total PCR inhibition samples by vaginal microorganisms feces Salmonella various body fluids immunomagnetic enterica separation feces Various enteric unknown size exclusion viruses chromatography, physicochemical extraction clinical Herpes simplex endogenous inhibitors, random repurification, specimens virus effects coamplified positive control feces Escherichia nonspecific inhibitors, urea, additional primers and coli hemoglobin, heparin, phenol, reaction cyclers, booster SDS PCR tissue culture Cytomegalovirus glove powder HIV suspensions, Mycobacterium mercury-based fixatives, reduced fixation times, skin biopsies leprae neutral buffered formaline ethanol fixation clinical Mycobacterium unknown inhibitors in pus, physicochemical specimens tuberculosis tissue biopsies, sputum, pleural extraction fluid mammalian mammalian unknown contaminant of additional DNA tissue tissue genetics reverse transcriptase formalin- Hepatitus C ribonucleotide vanadyl phenol/chloroform fixed paraffin virus complexes extraction tissue nasopharyngeal Bordetella unknown inhibitors phenol/chloroform aspirates pertussis extraction and swabs human HIV type I detergents mineral oil mononuclear blood cells bloodstain human unidentified heme compound, BSA mitochondrial hemin DNA blood various heparin alternative polymerases and buffers, chelex, spermine, [Mg2+], glycerol, BSA, heparinase sputa Mycoplasma N-acetyl-L-cysteine, pneumonia dithiothreitol, mucolytic agents human tissue HLA-DRB1 pollen, glove powder, impure genotyping DNA, heparin, hemoglobin clinical Mycobacterium unknown competitive internal specimens tuberculosis control dental plaque many unknown diatomaceous earth, guanidium isothiocyante, ethanol, acetone ancient Cytochrome b unknown ammonium acetate, mammalian gene ethidium bromide tissues

Polymerase chain reaction amplification of DNA or cDNA is a tried and trusted methodology; however, as discussed above, polymerases are inhibited by agents contained in crude samples, including but not limited to commonly used anticoagulants and hemoglobin. Recently mutant Taq polymerases have been engineered to harbor resistance to common inhibitors found in blood and soil. Currently available polymerases, e.g., HemoKlenTaq™ (New England BioLabs, Inc., Ipswich, Mass.) as well as OmniTaq™ and OmniKlenTaq™ (DNA Polymerase Technology, Inc., St. Louis, Mo.) are mutant (e.g., N-terminal truncation and/or point mutations) Taq polymerase that render them capable of amplifying DNA in the presence of up to 10%, 20% or 25% whole blood, depending on the product and reaction conditions (See, e.g., Kermekchiev et al. Nucl. Acids Res. 31:6139 (2003); and Kermekchiev et al., Nucl. Acid. Res., 37:e40 (2009); and see U.S. Pat. No. 7,462,475). Additionally, Phusion® Blood Direct PCR Kits (Finnzymes Oy, Espoo, Finland), include a unique fusion DNA polymerase enzyme engineered to incorporate a double-stranded DNA binding domain, which allows amplification under conditions which are typically inhibitory to conventional polymerases such as Taq or Pfu, and allow for amplification of DNA in the presence of up to about 40% whole blood under certain reaction conditions. See Wang et al., Nuc. Acids Res. 32:1197 (2004); and see U.S. Pat. Nos. 5,352,778 and 5,500,363. Furthermore, Kapa Blood PCR Mixes (Kapa Biosystems, Woburn, Mass.), provide a genetically engineered DNA polymerase enzyme which allows for direct amplification of whole blood at up to about 20% of the reaction volume under certain reaction conditions. Despite these breakthroughs, direct optical detection of generated amplicons is not possible with existing methods since fluorescence, absorbance, and other light based methods yield signals that are quenched by the presence of blood. See Kermekchiev et al., Nucl. Acid. Res., 37:e40 (2009).

We have found that complex samples such as whole blood can be directly amplified using about 5%, about 10%, about 20%, about 25%, about 30%, about 25%, about 40%, and about 45% or more whole blood in amplification reactions, and that the resulting amplicons can be directly detected from amplification reaction using magnetic resonance (MR) relaxation measurements upon the addition of conjugated magnetic particles bound to oligonucleotides complementary to the target nucleic acid sequence. Alternatively, the magnetic particles can be added to the sample prior to amplification. Thus, provided are methods for the use of nucleic acid amplification in a complex dirty sample, hybridization of the resulting amplicon to paramagnetic particles, followed by direct detection of hybridized magnetic particle conjugate and target amplicons using magnetic particle based detection systems. In particular embodiments, direct detection of hybridized magnetic particle conjugates and amplicons is via MR relaxation measurements (e.g., T₂, T₁, T1/T2 hybrid, T₂*, etc). Further provided are methods which are kinetic, in order to quantify the original nucleic acid copy number within the sample (e.g., sampling and nucleic acid detection at pre-defined cycle numbers, comparison of endogenous internal control nucleic acid, use of exogenous spiked homologous competitive control nucleic acid).

The terms “amplification” or “amplify” or derivatives thereof as used herein mean one or more methods known in the art for copying a target or template nucleic acid, thereby increasing the number of copies of a selected nucleic acid sequence. Amplification may be exponential or linear. A target or template nucleic acid may be either DNA or RNA. The sequences amplified in this manner form an “amplified region” or “amplicon.” Primer probes can be readily designed by those skilled in the art to target a specific template nucleic acid sequence. In certain preferred embodiments, resulting amplicons are short to allow for rapid cycling and generation of copies. The size of the amplicon can vary as needed to provide the ability to discriminate target nucleic acids from non-target nucleic acids. For example, amplicons can be less than about 1,000 nucleotides in length. Desirably the amplicons are from 100 to 500 nucleotides in length (e.g., 100 to 200, 150 to 250, 300 to 400, 350 to 450, or 400 to 500 nucleotides in length).

While the exemplary methods described hereinafter relate to amplification using polymerase chain reaction (“PCR”), numerous other methods are known in the art for amplification of nucleic acids (e.g., isothermal methods, rolling circle methods, etc.). Those skilled in the art will understand that these other methods may be used either in place of, or together with, PCR methods. See, e.g., Saiki, “Amplification of Genomic DNA” in PCR Protocols, Innis et al., Eds., Academic Press, San Diego, Calif., pp 13-20 (1990); Wharam et al., Nucleic Acids Res. 29:E54 (2001); Hafner et al., Biotechniques, 30:852 (2001). Further amplification methods suitable for use with the present methods include, for example, polymerase chain reaction (PCR) method, reverse transcription PCR (RT-PCR), ligase chain reaction (LCR), transcription based amplification system (TAS), transcription mediated amplification (TMA), nucleic acid sequence based amplification (NASBA) method, the strand displacement amplification (SDA) method, the loop mediated isothermal amplification (LAMP) method, the isothermal and chimeric primer-initiated amplification of nucleic acid (ICAN) method, and the smart amplification system (SMAP) method. These methods, as well as others are well known in the art and can be adapted for use in conjunction with provided methods of detection of amplified nucleic acid.

The PCR method is a technique for making many copies of a specific template DNA sequence. The PCR process is disclosed in U.S. Pat. Nos. 4,683,195; 4,683,202; and 4,965,188, each of which is incorporated herein by reference. One set of primers complementary to a template DNA are designed, and a region flanked by the primers is amplified by DNA polymerase in a reaction including multiple amplification cycles. Each amplification cycle includes an initial denaturation, and up to 50 cycles of annealing, strand elongation (or extension) and strand separation (denaturation). In each cycle of the reaction, the DNA sequence between the primers is copied. Primers can bind to the copied DNA as well as the original template sequence, so the total number of copies increases exponentially with time. PCR can be performed as according to Whelan, et al, Journal of Clinical Microbiology, 33:556 (1995). Various modified PCR methods are available and well known in the art. Various modifications such as the “RT-PCR” method, in which DNA is synthesized from RNA using a reverse transcriptase before performing PCR; and the “TaqMan PCR” method, in which only a specific allele is amplified and detected using a fluorescently labeled TaqMan probe, and Taq DNA polymerase, are known to those skilled in the art. RT-PCR and variations thereof have been described, for example, in U.S. Pat. Nos. 5,804,383; 5,407,800; 5,322,770; and 5,310,652, and references described therein, which are hereby incorporated by reference; and TaqMan PCR and related reagents for use in the method have been described, for example, in U.S. Pat. Nos. 5,210,015; 5,876,930; 5,538,848; 6,030,787; and 6,258,569, which are hereby incorporated by reference.

LCR is a method of DNA amplification similar to PCR, except that it uses four primers instead of two and uses the enzyme ligase to ligate or join two segments of DNA. Amplification can be performed in a thermal cycler (e.g., LCx of Abbott Labs, North Chicago, Ill.). LCR can be performed for example, as according to Moore et al., Journal of Clinical Microbiology 36:1028 (1998). LCR methods and variations have been described, for example, in European Patent Application Publication No. EP0320308, and U.S. Pat. No. 5,427,930, each of which is incorporated herein by reference.

The TAS method is a method for specifically amplifying a target RNA in which a transcript is obtained from a template RNA by a cDNA synthesis step and an RNA transcription step. In the cDNA synthesis step, a sequence recognized by a DNA-dependent RNA polymerase (i.e., a polymerase-binding sequence or PBS) is inserted into the cDNA copy downstream of the target or marker sequence to be amplified using a two-domain oligonucleotide primer. In the second step, an RNA polymerase is used to synthesize multiple copies of RNA from the cDNA template. Amplification using TAS requires only a few cycles because DNA-dependent RNA transcription can result in 10-1000 copies for each copy of cDNA template. TAS can be performed according to Kwoh et al., PNAS 86:1173 (1989). The TAS method has been described, for example, in International Patent Application Publication No. W01988/010315, which is incorporated herein by reference.

Transcription mediated amplification (TMA) is a transcription-based isothermal amplification reaction that uses RNA transcription by RNA polymerase and DNA transcription by reverse transcriptase to produce an RNA amplicon from target nucleic acid. TMA methods are advantageous in that they can produce 100 to 1000 copies of amplicon per amplification cycle, as opposed to PCR or LCR methods that produce only 2 copies per cycle. TMA has been described, for example, in U.S. Pat. No. 5,399,491 which is incorporated herein by reference. NASBA is a transcription-based method which for specifically amplifying a target RNA from either an RNA or DNA template. NASBA is a method used for the continuous amplification of nucleic acids in a single mixture at one temperature. A transcript is obtained from a template RNA by a DNA-dependent RNA polymerase using a forward primer having a sequence identical to a target RNA and a reverse primer having a sequence complementary to the target RNA a on the 3′ side and a promoter sequence that recognizes T7 RNA polymerase on the 5′ side. A transcript is further synthesized using the obtained transcript as template. This method can be performed as according to Heim, et al., Nucleic Acids Res., 26:2250 (1998). The NASBA method has been described in U.S. Pat. No. 5,130,238, which is incorporated herein by reference.

The SDA method is an isothermal nucleic acid amplification method in which target DNA is amplified using a DNA strand substituted with a strand synthesized by a strand substitution type DNA polymerase lacking 5′->3′ exonuclease activity by a single stranded nick generated by a restriction enzyme as a template of the next replication. A primer containing a restriction site is annealed to template, and then amplification primers are annealed to 5′ adjacent sequences (forming a nick). Amplification is initiated at a fixed temperature. Newly synthesized DNA strands are nicked by a restriction enzyme and the polymerase amplification begins again, displacing the newly synthesized strands. SDA can be performed according to Walker, et al., PNAS, 89:392 (1992). SDA methods have been described in U.S. Pat. Nos. 5,455,166 and 5,457,027, each of which are incorporated by reference.

The LAMP method is an isothermal amplification method in which a loop is always formed at the 3′ end of a synthesized DNA, primers are annealed within the loop, and specific amplification of the target DNA is performed isothermally. LAMP can be performed according to Nagamine et al., Clinical Chemistry. 47:1742 (2001). LAMP methods have been described in U.S. Pat. Nos. 6,410,278; 6,974,670; and 7,175,985, each of which are incorporated by reference.

The ICAN method is anisothermal amplification method in which specific amplification of a target DNA is performed isothermally by a strand substitution reaction, a template exchange reaction, and a nick introduction reaction, using a chimeric primer including RNA-DNA and DNA polymerase having a strand substitution activity and RNase H. ICAN can be performed according to Mukai et al., J. Biochem. 142: 273 (2007). The ICAN method has been described in U.S. Pat. No. 6,951,722, which is incorporated herein by reference.

The SMAP (MITANI) method is a method in which a target nucleic acid is continuously synthesized under isothermal conditions using a primer set including two kinds of primers and DNA or RNA as a template. The first primer included in the primer set includes, in the 3′ end region thereof, a sequence (Ac′) hybridizable with a sequence (A) in the 3′ end region of a target nucleic acid sequence as well as, on the 5′ side of the above-mentioned sequence (Ac′), a sequence (B′) hybridizable with a sequence (Bc) complementary to a sequence (B) existing on the 5′ side of the above-mentioned sequence (A) in the above-mentioned target nucleic acid sequence. The second primer includes, in the 3′ end region thereof, a sequence (Cc′) hybridizable with a sequence (C) in the 3′ end region of a sequence complementary to the above-mentioned target nucleic acid sequence as well as a loopback sequence (D-Dc′) including two nucleic acid sequences hybridizable with each other on an identical strand on the 5′ side of the above-mentioned sequence (Cc′). SMAP can be performed according to Mitani et al., Nat. Methods, 4(3): 257 (2007). SMAP methods have been described in U.S. Patent Application Publication Nos. 2006/0160084, 2007/0190531 and 2009/0042197, each of which is incorporated herein by reference.

The amplification reaction can be designed to produce a specific type of amplified product, such as nucleic acids that are double stranded; single stranded; double stranded with 3′ or 5′ overhangs; or double stranded with chemical ligands on the 5′ and 3′ ends. The amplified PCR product can be detected by: (i) hybridization of the amplified product to magnetic particle bound complementary oligonucleotides, where two different oligonucleotides are used that hybridize to the amplified product such thatthe nucleic acid serves as an interparticle tether promoting particle agglomeration; (ii) hybridization mediated detection where the DNA of the amplified product must first be denatured; (iii) hybridization mediated detection where the particles hybridize to 5′ and 3′ overhangs of the amplified product; (iv) binding of the particles to the chemical or biochemical ligands on the termini of the amplified product, such as streptavidin functionalized particles binding to biotin functionalized amplified product.

The systems and methods of the invention can be used to perform real time PCR and provide quantitative information about the amount of target nucleic acid present in a sample (see FIG. 52 and Example 18). Methods for conducting quantitative real time PCR are provided in the literature (see for example: RT-PCR Protocols. Methods in Molecular Biology, Vol. 193. Joe O'Connell, ed. Totowa, N.J.: Humana Press, 2002, 378 pp. ISBN 0-89603-875-0.). Example 18 describes use of the methods of the invention for real time PCR analysis of a whole blood sample.

The systems and methods of the invention can be used to perform real time PCR directly in opaque samples, such as whole blood, using magnetic nanoparticles modified with capture probes and magnetic separation. Using real-time PCR allows for the quantification of a target nucleic acid without opening the reaction tube after the PCR reaction has commenced.

In one approach, biotin or avidin labeled primers can be used to perform real-time PCR. These labels would have corresponding binding moieties on the magnetic particles that could have very fast binding times. This allows for a double stranded product to be generated and allows for much faster particle binding times, decreasing the overall turnaround time. The binding chemistry would be reversible, preventing the primers from remaining particle bound. In order to reverse the binding, the sample can be heated or the pH adjusted.

In another approach, the real-time PCR can be accomplished through the generation of duplex DNA with overhangs that can hybridize to the superparamagnetic particles. Additionally, LNA and/or fluorinated capture probes may speed up the hybridization times. An exemplary set of capture probes useful in this method is set forth in the table below:

Pan Candida F Uni-Tail 5′- CAT GAT CTG CTG CAG/iSp18/GG CAT GCC TGT TTG AGC GTC -3′ (SEQ ID NO. 19) Pan Candida R Uni-Tail 5′- GCA GAA CTC CAG ACC/iSp18/GC TTA TTG ATA TGC TTA AGT TCA GCG GGT -3′ (SEQ ID NO. 20) 3′AM universal tail CP 5′- CTG CAG CAG ATC ATG TTT TTT TTT TTT/3AmMO/-3′ (SEQ ID NO. 21) 5′AM universal tail CP 5′-/5AmMC6/TT TTT TTT TTT TGG TCT GGA GTT CTG C -3′ Fluorinated 3′AM uni CP 5′- CTG/i2FC/AG/i2FC/AG/i2FA/TC/i2FA/TG TTT TTT TTT TTT/3AmMO/ -3′ (SEQ ID NO. 22) Fluorinated 5′AM uni CP 5′-/5AmMC12/TT TTT TTT TTT TGG T/i2FC/T G/i2FG/ AG/i2FU/T CTG C -3′ (SEQ ID NO. 23)

In still another approach, the particles are designed to have a hairpin that buries the binding site to the amplicon. Heating the particles to a higher melt temperature would expose the binding site of the hairpin to allow binding to the target.

In another approach, a probe that hybridizes to an amplicon is tethering two (or more) particles. The reaction would be conducted in the presence of a polymerase with 5′ exonuclease activity, resulting in the cleavage of the inter-particle tether and a subsequent change in T2. The polymerase is selected to have exonuclease activity and compatibility with the matrix of choice (e.g. blood). In this approach, smaller particles (e.g., 30 nm CLIO) can be used to reduce steric hindrance of the hybridization to target or subsequent enzymatic digestion during polymerization (see, e.g., Heid et al Genome Research 1996 6: 986-994).

In another approach, two particle populations can be synthesized to bear complementary capture probes. In the absence of amplicon, the capture probes hybridize promoting particle clustering. Upon generation of amplicon, the amplicon can compete, hybridize, and displace the capture probes leading to particle declustering. The method can be conducted in the presence or absence of nanoparticles. The particles free in solution will cluster and decluster due to the thermocycling (because, e.g., the Tm can be below 95° C.). The Tm of the amplicon binding to one of the particle-immobilized capture probes can be designed such that that binding interaction is more favorable than the particle-to-particle binding interaction (by, e.g., engineering point mutations within the capture probes to thermodynamically destabilize the duplexes). In this embodiment, the particle concentration can be kept at, e.g., low or high levels. Examples of probes and primers useful in such a system are set forth in the table below.

C. albicans ITS2 Reverse P 5′- CCG TCT TTC AAG CAA ACC CAA GTC G -3′ (SEQ ID NO. 24) C. albicans ITS2 Forward P 5′- TTT CTC CCT CAA ACC GCT GG -3′ (SEQ ID NO. 25) C. alb ITS2 CP1 5′-/5AmMC12/TT TTT TTT TTT TTT TGG TTT GGT GTT GAG CAA TAC G -3′ (SEQ ID NO. 26) C. alb ITS2 CP2 5′-/5AmMC12/TT TTT TTT TTT TCG TAT TGC TCA ACA CCA AAC C -3′ (SEQ ID NO. 27) C. alb ITS2 Long CP1 5′-/5AmMC12/TT TTT TTT TTT TTT TAC CGC TGG GTT TGG TGT TGA GCA ATA CG -3′ (SEQ ID NO. 28) C. alb ITS2 Long CP2 5′-/5AmMC12/TT TTT TTT TTT TTT TAC CGC TGG GTT TGG TGT TGA GCA ATA CG -3′ (SEQ ID NO. 29) C. alb ITS2 mut 3 CP1 5′-/5AmMC12/TT TTT TTT TTT TGG TTT GGC GTA GAG CCA TAC G -3′ (SEQ ID NO. 30) C. alb ITS2 mut 4 CP1 5′-/5AmMC12/TT TTT TTT TTT TGG TCT GGC GTA GAG CCA TAC G -3′ (SEQ ID NO. 31)

Previous work showed that in some cases the presence of particles in the PCR reaction could inhibit PCR. For these inhibitory particles, it is envisioned that the particles could be pulled to the side of the tube (or other location within the container) to keep them out of solution during the PCR reaction. Methods can be used to release the particles back into suspension to allow them to hybridize to the PCR product and then pull them back out of solution.

In certain embodiments, the invention features the use of enzymes compatible with whole blood, e.g., NEB Hemoklentaq, DNAP Omniklentaq, Kapa Biosystems whole blood enzyme, Thermo-Fisher Finnzymes Phusion enzyme.

The invention also features quantitative asymmetric PCR. In any of the real-time PCR methods of the invention, the method can involve the following steps:

-   -   1. aliquoting whole blood into a prepared PCR mastermix         containing superparamagnetic particles;     -   2. prior to the first PCR cycle, closing the tube until PCR         cycling is completed;     -   3. loading the tube onto thermal cycler;     -   4. running “n” cycles of standard PCR thermal cycling;     -   5. conducting a T2 detection (the exact time duration and steps         for this vary depending on the biochemical and particle design         approach described below); and     -   6. repeating steps 4 and 5 until enough T2 readings have been         taken for an accurate quantification of initial target         concentration.

The above methods can be used with any of the following categories of detection of aggregation or disaggregation described herein, including:

Name Description Clustering-based Particles >100 nm or magnetic-separation compatible. detection and Particles removed from solution during PCR magnetic T2 goes up with amplicon generation separation Agitation during step 5 Clustering-based Particles >100 nm detection with Particles do not inhibit PCR particles >100 nm T2 goes up with amplicon generation Agitation during step 5 De-clustering- Particles >100 nm based detection Particles on the side of the tube during PCR and magnetic T2 goes down with amplicon generation separation Agitation during step 5 De-clustering- Particles >100 nm based detection Particles do not inhibit PCR with particles T2 goes down with amplicon generation >100 nm Agitation during step 5 Clustering-based Particles <100 nm (e.g., 30 nm particles) detection with T2 goes down with amplicon appearance (at least for particles <100 nm initial cycles, T2 may subsequently increase as cluster size increases) Has potential for much more rapid hybridization times No agitation required to keep particles suspended Particle concentration in nM range De-clustering- Particles <100 nm (e.g., 30 nm particles) based detection T2 goes up with amplicon appearance with particles T2 could decrease as the cluster size increase above <100 nm 100 nm No agitation required to keep particles suspended Has potential for most rapid detection times Particle concentration in nM range

A variety of impurities and components of whole blood can be inhibitory to the polymerase and primer annealing. These inhibitors can lead to generation of false positives and low sensitivities. To reduce the generation of false positives and low sensitivities when amplifying and detecting nucleic acids in complex samples, it is desirable to utilize a thermal stable polymerase not inhibited by whole blood samples (see, e.g., U.S. Pat. No. 7,462,475) and include one or more internal PCR assay controls (see Rosenstraus et al. J. Clin Microbiol. 36:191 (1998) and Hoofar et al., J. Clin. Microbiol. 42:1863 (2004)). For example, to assure that clinical specimens are successfully amplified and detected, the assay can include an internal control nucleic acid that contains primer binding regions identical to those of the target sequence. As shown in the examples, the target nucleic acid and internal control can be selected such that each has a unique probe binding region that differentiates the internal control from the target nucleic acid. The internal control is, optionally, employed in combination with a processing positive control, a processing negative control, and a reagent control for the safe and accurate determination and identification of an infecting organism in, e.g., a whole blood clinical sample. The internal control can be an inhibition control that is designed to co-amplify with the nucleic acid target being detected. Failure of the internal inhibition control to be amplified is evidence of a reagent failure or process error. Universal primers can be designed such that the target sequence and the internal control sequence are amplified in the same reaction tube. Thus, using this format, if the target DNA is amplified but the internal control is not it is then assumed that the target DNA is present in a proportionally greater amount than the internal control and the positive result is valid as the internal control amplification is unnecessary. If, on the other hand, neither the internal control nor the target is amplified it is then assumed that inhibition of the PCR reaction has occurred and the test for that particular sample is not valid. The assays of the invention can include one or more positive processing controls in which one or more target nucleic acids is included in the assay (e.g., each included with one or more cartridges) at 3× to 5× the limit of detection. The measured T2 for each of the positive processing controls must be above the pre-determined threshold indicating the presence of the target nucleic acid. The positive processing controls can detect all reagent failures in each step of the process (e.g., lysis, PCR, and T2 detection), and can be used for quality control of the system. The assays of the invention can include one or more negative processing controls consisting of a solution free of target nucleic acid (e.g., buffer alone). The T2 measurements for the negative processing control should be below the threshold indicating a negative result while the T2 measured for the internal control is above the decision threshold indicating an internal control positive result. The purpose of the negative control is to detect carry-over contamination and/or reagent contamination. The assays of the invention can include one or more reagent controls. The reagent control will detect reagent failures in the PCR stage of the reaction (i.e. incomplete transfer of master mix to the PCR tubes). The reagent controls can also detect gross failures in reagent transfer prior to T2 detection.

Contamination Control

One of the major problems in the use of PCR as an analytical tool is the risk of having new reactions contaminated with old, amplified products. Potential sources of contamination include a) large numbers of target organisms in clinical specimens that may result in cross-contamination, b) plasmid clones derived from organisms that have been previously analyzed and that may be present in larger numbers in the laboratory environment, and c) repeated amplification of the same target sequence leading to accumulation of amplification products in the laboratory environment. A common source of the accumulation of the PCR amplicon is aerosolization of the product. Typically, if uncontrolled aerosolization occurs, the amplicon will contaminate laboratory reagents, equipment, and ventilation systems. When this happens, all reactions will be positive, and it is not possible to distinguish between amplified products from the contamination or a true, positive sample. In addition to taking precautions to avoid or control this carry-over of old products, it is necessary to include a blank reference reaction in every PCR experiment to check for carry-over. In order to be certain that all results are reliable, there must be no amplified products after the temperature cycling. A carry-over contamination will be visible on the agarose gel as faint bands. Furthermore, it is also very important to include a positive sample. If, contrary to expectation, the sample is negative, none of the results can be considered as trustworthy. (see Aslanzadeh et al., Annals of Clin Lab Science, 34:389 (2004)).

It is conceivable that the reagents used to prepare the PCR may be contaminated. After the amplification a positive sample may contain 250 ng PCR product in 50 μl. This gives a total of 3.9 1011 copies of a 600 bp double-stranded product. One thousandth of a microliter of this reaction will contain approximately 8 million copies. If a very small and invisible aerosol is formed when the PCR vessel is opened, there is a possibility that this aerosol can contain a very large number of amplified products. Furthermore, the microscopic droplets in an aerosol are able to float for a long time in the air, and if there is turbulence in the room, they can be carried a long way. Considering the fact that only one copy is enough to create a false positive reaction, it is obvious that great care must be taken to avoid this carry-over contamination.

To address the problem of contamination problem, one or more of the following protocols can be used:

(i) Replace all reagents and stock buffers with new chemicals and new water which have never been in contact with the areas of sample preparation and PCR analysis.

(ii) Physically divide the area of reagent mixing and sample preparation from the area of product analysis (Kwok & Higuchi, Nature, 339:237 (1989)).

(iii) Sample preparation workstations can be cleaned (e.g., with 10% sodium hypochlorite solution, followed by removal of the bleach with ethanol). Oxidative breakdown of nucleic acids prevents reamplification of impurities in subsequent PCR reactions.

(iv) Sterilization of the amplification products ensures that subsequent diagnostic assays are not compromised by carryover DNA, and must follow two generally accepted criteria: (a) the PCR needs to be exposed to the environment after there has been some form of modification of amplicon, and (b) the modification must not interfere with the detection method. For example, UV irradiation can effectively remove contaminating DNA (see Rys et al., J. Clin Microbiol. 3:2356 (1993); and Sarker et al., Nature, 343:27 (1990)), but the irradiation of the PCR reagents must take place before addition of polymerase, primers, and template DNA. Furthermore, this approach may be inefficient because the large numbers of mononucleotides present in the reaction will absorb much of the UV light (See Frothingham et al., BioTechniques 13:208 (1992)). UV light sterilization of the amplification products uses the property of UV light to induce thymine dimmers and other covalent modifications of the DNA that render the contaminating DNA un-amplifiable. Alternatively, incorporation of dUTP into the amplified fragments will also alter the composition of the product so that it is different from the template DNA composition (see Longo et al., Gene 93:125 (1990); and U.S. Pat. Nos. 5,035,996; 7,687,247; and 5,418,149). The enzyme Uracil-N-Glycosylase (UNG) is added together with the normal PCR enzyme to the reaction mix. The UNG enzyme will cleave the uracil base from DNA strands before amplification, and leave all the old amplified products unable to act as templates for new amplification, but will not react on unincorporated dUTP or new template. This will efficiently remove contaminating PCR products from the reaction after the PCR vessel has been closed, and thus no new contamination is possible. However, the use of dUTP in PCR reactions to prevent carry-over can cause problems when the products are used in a later hybridization study, due to the low capability of uracil to act in hybridization (Carmody et al., Biotechniques 15:692 (1993)). dUTP is incorporated instead of dTTP. When a probe rich in T's is amplified with the substitution of dTTP for dUTP in the reaction mixture, a later hybridization signal with the probe may be eliminated. To avoid the decrease in hybridization signal the probe binding site should be chosen with no more than 25% T's, and without stretches of poly-T. Furthermore, the PCR should contain equal concentrations of dUTP and dTTP and not only dUTP. In contrast to the decrease in hybridization signal is the increase in product amplification when using dUTP, especially when AT-rich target sequences are selected. This is probably because the incorporation of dUTP decreases re-annealing of formed PCR products which would prevent primers from annealing. If this approach is used to increase the product yield, the primer binding sites should be selected with a low content of T's, since primer annealing also will be inhibited by dUTP incorporation (Carmody et al., Biotechniques 15:692 (1993)). Heat labile UDG isolated from BMTU 3346 is described in Schmidt et al. Biochemica 2:13 (1996) (see also U.S. Pat. No. 6,187,575). A uracil-DNA glycosylase gene from Psychrobacter sp HJ147 was described in U.S. Pat. No. 7,723,093. Lastly a cod uracil-DNA glycosylase was described (U.S. Pat. No. 7,037,703).

(v) DNase digestion after PCR can be used to reduce contamination. A heat labile DNase enzyme was identified that can be used to digest dsDNA to remove any contaminating DNA prior to the PCR amplification step of the target DNA. In this case, the ds DNA is digested, the sample is heated to inactivate the DNase, and the target sample and PCR reactants are added to the reaction tube to carry out the target specific PCR. (see U.S. Pat. No. 6,541,204).

(vi) Sterilization after PCR can be used to reduce contamination. Incorporation of a photochemical reagent (isopsoralen) into the product during amplification will create a difference in composition between the template DNA and the amplified PCR products (see Rys et al., J. Clin Microbiol. 3:2356 (1993)). Furocoumarin compounds, such as isopsoralen or psoralen, are a class of planar tricylcic reagents that are known to intercalate between base pairs of nucleic acids (see U.S. Pat. No. 5,532,145). Light treatment of the closed PCR vessel will render previously formed PCR products unable to act as templates for further amplification. The hybridization abilities of the product are not changed, but the detection capabilities on agarose gel can be decreased due to reduced binding of EtBr. Isopsoralen of 25 mg/ml was shown to be ineffective at preventing contamination, and at concentrations up to 100 mg/ml, isopsoralen may have an inhibitory effect on the PCR reaction itself (see U.S. Pat. No. 5,221,608). Alternatively, primer hydrolysis can be used to sterilize a reaction after amplification. Primer hydrolysis of sterilization of amplification products relies on the uniquely synthesized chimeric primers that contain one or more ribose linkages at the 3′ end. The generated amplification products containing those ribose residues are susceptible to alkaline hydrolysis at the site of the ribose molecule. The method includes exposure to 1M NaOH and incubated for 30 minutes to hydrolyze the amplification products at the sites of the incorporated ribose. Thus, if there is carryover contamination, the old amplicon has lost its primer site due to the hydrolysis of the ribose molecules and the new amplicon will have the primer binding sites. In another approach, addition of hydroxylamine hydrochloride to PCR reaction tubes after amplification sterilizes the reaction contents, and is especially effective for short (<100 bp) and GC rich amplification products. The hydroxylamine preferentially reacts with oxygen atoms in the cytosine residues and creates covalent adducts that prevent base-pairing with guanine residues in subsequent reactions. Thus, the modified amplification product are not recognized as amplification targets in subsequent PCR reactions.

(vii) Prevention of carry-over by changing the product composition from the template can reduce contamination. In one approach the DNA composition of the PCR product can be different from the natural template DNA composition. This altered composition is intended to make the PCR products sensitive to treatment that will not alter the template DNA. The treatment of the closed PCR vessel just before amplification should make the contaminating PCR product unable to participate in the amplification. Here the modification would have to be innocuous to the detection method. The types of modifications that can be useful in distinguishing contaminant amplification product will be apparent, but include introduction of a ligand, cross-linking agent, enzyme recognition site, or other cleavable moiety (See U.S. Pat. Nos. 5,427,929; 5,650,302; 5,876,976; and 6,037,152).

One or more of the methods described above can be used in conjunction with the methods of the invention to reduce the risk of contamination and false positives. Carry-over of old amplified PCR products can be a very serious risk in the nucleic acid analysis in the T2 Biosystems diagnostic platform. One way to prevent this contamination is to physically divide the PCR working areas. Alternatives to the physical separation of the PCR reaction method include UV irradiation of PCR mix and incorporation of reagents into the newly formed PCR product can be used to alter it from the template.

Cartridge Units

The systems for carrying out the methods of the invention can include one or more cartridge units to provide a convenient method for placing all of the assay reagents and consumables onto the system. For example, the system may be customized to perform a specific function, or adapted to perform more than one function, e.g., via changeable cartridge units containing arrays of micro wells with customized magnetic particles contained therein. The system can include a replaceable and/or interchangeable cartridge containing an array of wells pre-loaded with magnetic particles, and designed for detection and/or concentration measurement of a particular analyte. Alternatively, the system may be usable with different cartridges, each designed for detection and/or concentration measurements of different analytes, or configured with separate cartridge modules for reagent and detection for a given assay. The cartridge may be sized to facilitate insertion into and ejection from a housing for the preparation of a liquid sample which is transferred to other units in the system (i.e., a magnetic assisted agglomeration unit, or an NMR unit). The cartridge unit itself could potentially interface directly with manipulation stations as well as with the MR reader(s). The cartridge unit can be a modular cartridge having an inlet module that can be sterilized independent of the reagent module.

For handling biological samples, such as blood samples, there are numerous competing requirements for the cartridge design, including the need for sterility for the inlet module to prevent cross contamination and false positive test results, and the need to include reagents in the package which cannot be easily sterilized using standard terminal sterilization techniques like irradiation. An inlet module for sample aliquoting can be designed to interface with uncapped vacutainer tubes, and to aliquot two a sample volume that can be used to perform, for example, a candida assay (see FIGS. 7D-7F). The vacutainer permits a partial or full fill. The inlet module has two hard plastic parts, that get ultrasonically welded together and foil sealed to form a network of channels to allow a flow path to form into the first well overflow to the second sample well. A soft vacutainer seal part is used to for a seal with the vacutainer, and includes a port for sample flow, and a venting port. To overcome the flow resistance once the vacutainer is loaded and inverted, some hydrostatic pressure is needed. Every time sample is removed from a sample well, the well will get replenished by flow from the vacutainer.

A modular cartridge can provide a simple means for cross contamination control during certain assays, including but not limited to distribution of PCR products into multiple detection aliquots. In addition, a modular cartridge can be compatible with automated fluid dispensing, and provides a way to hold reagents at very small volumes for long periods of time (in excess of a year). Finally, pre-dispensing these reagents allows concentration and volumetric accuracy to be set by the manufacturing process and provides for a point of care use instrument that is more convenient as it can require much less precise pipetting.

The modular cartridge of the invention is a cartridge that is separated into modules that can be packaged and if necessary sterilized separately. They can also be handled and stored separately, if for example the reagent module requires refrigeration but the detection module does not. FIG. 6 shows a representative cartridge with an inlet module, a reagent module and a detection module that are snapped together. In this embodiment, the inlet module would be packaged separately in a sterile package and the reagent and detection modules would be pre-assembled and packaged together.

During storage, the reagent module could be stored in a refrigerator while the inlet module could be stored in dry storage. This provides the additional advantage that only a very small amount of refrigerator or freezer space is required to store many assays. At time of use, the operator would retrieve a detection module and open the package, potentially using sterile technique to prevent contamination with skin flora if required by the assay. The Vacutainer tube is then decapped and the inverted inlet module is placed onto the tube as shown in FIG. 7A. This module has been designed to be easily moldable using single draw tooling as shown in FIGS. 7B and 7C and the top and bottom of the cartridge are sealed with foil to prevent contamination and also to close the channels. Once the tube has been re-sealed using the inlet module, the assembly is turned right side up and snapped onto the remainder of the cartridge. The inlet section includes a well with an overflow that allows sample tubes with between 2 and 6 ml of blood to be used and still provide a constant depth interface to the system automation. It accomplishes this by means of the overflow shown in FIG. 8, where blood that overflows the sampling well simply falls into the cartridge body, preventing contamination.

FIGS. 9A-9C show the means of storing precisely pipetted small volume reagents. The reagents are kept in pipette tips that are shown in FIG. 9C. These are filled by manufacturing automation and then are placed into the cartridge to seal their tips in tight fitting wells which are shown in a cutaway view FIG. 9B. Finally, foil seals are placed on the back of the tips to provide a complete water vapor proof seal. It is also possible to seal the whole module with a seal that will be removed by the operator, either in place of or in addition to the aforementioned foils. This module also provides storage for empty reaction vessels and pipette tips for use by the instrument while the detection module provides storage for capped 200 μl PCR vials used by the instrument to make final measurements from.

FIGS. 10-13C show an alternative embodiment of the detection module of the cartridge which is design to provide for contamination control during, for example, pipetting of post-PCR (polymerase chain reaction) products. This is required because the billion fold amplification produced by PCR presents a great risk of cross contamination and false positives. However, it is desirable to be able to aliquot this mixture safely, because low frequency analytes will have been amplified up and can be distributed for separate detection or identification. There are three ways in which this portion of the cartridge aids in contamination control during this aliquoting operation.

First, the cartridge contains a recessed well to perform the transfer operations in as shown in FIGS. 10A and 10B. Second, the machine provides airflow through this well and down into the cartridge through holes in the bottom of the well, as shown in FIG. 11. The depth of the well is such that a pipette tip will remain in the airflow and prevent any aerosol from escaping. FIG. 12 depicts a bottom view of the detection module, showing the bottom of the detection tubes and the two holes used to ensure airflow. An optional filter can be inserted here to capture any liquid aerosol and prevent it from entering the machine. This filter could also be a sheet of a hydrophobic material like Gore-tex that will allow air but not liquids to escape. Finally, there is a special seal cap on each 200 ul tube to provide a make then break seal for each pipette tip as it enters the vessel, as shown in FIGS. 13A-13C. It is contemplated that the pipette tip used for aliqouting be stored in this well at all, thus making it possible for the tip never to leave the controlled air flow region.

Alternatively, the modular cartridge is designed for a multiplexed assay. The challenge in multiplexing assays is combining multiple assays which have incompatible assay requirements (i.e., different incubation times and/or temperatures) on one cartridge. The cartridge format depicted in FIGS. 14A-14C allows for the combination of different assays with dramatically different assay requirements. The cartridge features two main components: (i) a reagent module (i.e., the reagent strip portion) that contains all of the individual reagents required for the full assay panel, and (ii) the detection module. The detection modules contain only the parts of the cartridge that carry through the incubation, and can carry single assays or several assays, as needed. The detection module depicted in FIG. 14B includes two detection chambers for a single assay, the first detection chamber as the control and the second detection chamber for the sample. This cartridge format is expandable in that additional assays can be added by including reagents and an additional detection module.

The operation of the module begins when the user inserts the entire or a portion of the cartridge into the instrument. The instruments performs the assay actuation, aliquoting the assays into the separate detection chambers. These individual detection chambers are then disconnected from the reagent strip and from each other, and progress through the system separately. Because the reagent module is separated and discarded, the smallest possible sample unit travels through the instrument, conserving internal instrument space. By splitting up each assay into its own unit, different incubation times and temperatures are possible as each multiplexed assay is physically removed from the others and each sample is individually manipulated.

The cartridge units of the invention can include one or more populations of magnetic particles, either as a liquid suspension or dried magnetic particles which are reconstituted prior to use. For example, the cartridge units of the invention can include a compartment including from 1×10⁶ to 1×10¹³ magnetic particles (e.g., from 1×10⁶ to 1×10⁸, 1×10⁷ to 1×10⁹, 1×10⁸ to 1×10¹⁰, 1×10⁹ to 1×10¹¹, 1×10¹⁰ to 1×10¹², 1×10¹¹ to 1×10¹³, or from 1×10⁷ to 5×10⁸ magnetic particles) for assaying a single liquid sample.

Agitation Units

The systems for carrying out the methods of the invention can include one or more agitation units to break apart non-specific magnetic particle interactions and re-distribute the magnetic particles back into the liquid sample, or to simply agitate the sample tube to completely mix the assay reagents. For example, the agitation units can include a sonication, vortexing, shaking, or ultrasound station for mixing one or more liquid samples. Mixing could be achieved by aspiration dispensing or other fluid motion (e.g., flow within a channel). Also, mixing could be provided by a vibrating pipette or a pipette that moves from side to side within the sample tube.

The agitation unit can be vortexer or a compact vortexer each of which can be designed to provide a stable motion for the desired sample mixing.

The vortexer includes the following components: (i) a sample support, (ii) a main plate, (iii) four linkages, (iv) linear rail and carriage system (×2), (v) a support for driveshaft and rails, (vi) coupling and driveshaft, (vii) a mounting plate, and (viii) a drive motor (see FIG. 20).

The compact vortexer includes the following components: (i) a sample support, (ii) a main plate, (iii) two linkages, (iv) linear rail and carriage system (×1), (v) a support for linear rail, (vi) support for driveshaft, (vii) coupling and driveshaft, (viii) a mounting plate, and (ix) a drive motor (see FIG. 21).

The basic principle of motion for a vortexer is as follows: the driveshaft including one axis coaxial to the motor shaft, and a second that is offset and parallel to the motor shaft. When the motor shaft is attached to the driveshaft (typically through a helical coupling) and rotated, the offset axis of the driveshaft is driven in an orbital path. The typical offset is ¼″ to produce a vortex in a single 0.2 mL sample tube, but this can be easily modified to effectively mix different sample volumes in other tube geometries.

Alternatively, the vortexer can be of the type utilizing a planetary belt drive (see FIGS. 23A-23C). FIG. 23A is an overall view showing the vortexer configured for 1 large tube. FIG. 23B is a section view showing 2 tube holders for small tubes. FIG. 23C is an overall view of vortexer showing 4 tubes and a close-up of planetary belt drive mechanism.

The drive motor is typically a servo or stepper with an encoder. These motors have an “index” mark that allows the motor to find a specific point in its rotation. These index marks are used to home the system, and ensure that the sample can be returned to a known position after mixing. Knowing the exact position of the sample in the vortex station allows theses vortexers to be easily accessed by robotic actuators and thus integrated into an automated system. In lieu of index marks, sensing devices external could be employed (see FIG. 22A). These could be mechanical, magnetic, optical or other sensor that is capable of resolving the sample's position at any point along the system's path or at a fixed “home” position. In order to access a vortexers or centrifuge via a robotic sample holder/positioned, the system can include using an index mark or external switch to “home” the system to a set position after running, using a sensor which tracks the sample motion at all times, so that wherever the system stops the robot knows the position, and using a “find” method that includes finding a sample after running that would employ a vision system that tracks the sample. The guide mechanism is depicted in FIG. 22B. The main plate is connected to the offset axis of the drive shaft and is free to rotate. The plate follows the orbital path around and dictated by the motor shaft. One end of a linkage is connected to the main plate, and is free to rotate. Therefore in this way, the connected linkage is then connected to the orbital rotation of the drive shaft. The other end of the linkage is connected to a carriage of the linear rail system and is free to rotate. Thus this end of the linkage follows the linear path of the rail. Having two linkages connected to both the carriage and main plate in this way prevents the main plate from rotating around its own center. In the vortexer, two linkages are used on two sides of the main plate (4 in total) to balance and stabilize the entire system.

The two vortexers differ because of their use and design requirements. The compact version is designed to occupy less space, and requires less durability than this version because it is run at a lower speed, as limited by its smaller motor. For these reasons only two linkages are used to connect to a single linear rail system in the compact vortexer. This version needs to be capable of higher speeds, and a nearly continuous utilization due to the large throughput capability of this system. For these reasons a second carriage and set of linkages is added to balance the system, and increase its durability.

Systems

The systems for carrying out the methods of the invention can include one or more NMR units, MAA units, cartridge units, and agitation units. Such systems may further include other components for carrying out an automated assay of the invention, such as a PCR unit for the detection of oligonucleotides; a centrifuge, a robotic arm for delivery an liquid sample from unit to unit within the system; one or more incubation units; a fluid transfer unit (i.e., pipetting device) for combining assay reagents and a biological sample to form the liquid sample; a computer with a programmable processor for storing data, processing data, and for controlling the activation and deactivation of the various units according to a one or more preset protocols; and a cartridge insertion system for delivering pre-filled cartridges to the system, optionally with instructions to the computer identifying the reagents and protocol to be used in conjunction with the cartridge. See FIG. 42.

The systems of the invention can provide an effective means for high throughput and real-time detection of analytes present in a bodily fluid from a subject. The detection methods may be used in a wide variety of circumstances including, without limitation, identification and/or quantification of analytes that are associated with specific biological processes, physiological conditions, disorders or stages of disorders. As such, the systems have a broad spectrum of utility in, for example, drug screening, disease diagnosis, phylogenetic classification, parental and forensic identification, disease onset and recurrence, individual response to treatment versus population bases, and monitoring of therapy. The subject devices and systems are also particularly useful for advancing preclinical and clinical stage of development of therapeutics, improving patient compliance, monitoring ADRs associated with a prescribed drug, developing individualized medicine, outsourcing blood testing from the central laboratory to the home or on a prescription basis, and monitoring therapeutic agents following regulatory approval. The devices and systems can provide a flexible system for personalized medicine. The system of the invention can be changed or interchanged along with a protocol or instructions to a programmable processor of the system to perform a wide variety of assays as described herein. The systems of the invention offer many advantages of a laboratory setting contained in a desk-top or smaller size automated instrument.

The systems of the invention can be used to simultaneously assay analytes that are present in the same liquid sample over a wide concentration range, and can be used to monitor the rate of change of an analyte concentration and/or or concentration of PD or PK markers over a period of time in a single subject, or used for performing trend analysis on the concentration, or markers of PD, or PK, whether they are concentrations of drugs or their metabolites. For example, if glucose were the analyte of interest, the concentration of glucose in a sample at a given time as well as the rate of change of the glucose concentration over a given period of time could be highly useful in predicting and avoiding, for example, hypoglycemic events. Thus, the data generated with the use of the subject fluidic devices and systems can be utilized for performing a trend analysis on the concentration of an analyte in a subject.

For example, a patient may be provided with a plurality of cartridge units to be used for detecting a variety of analytes at predetermined times. A subject may, for example, use different cartridge units on different days of the week. In some embodiments the software on the system is designed to recognize an identifier on the cartridge instructing the system computer to run a particular protocol for running the assay and/or processing the data. The protocols on the system can be updated through an external interface, such as an USB drive or an Ethernet connection, or in some embodiments the entire protocol can be recorded in the barcode attached to the cartridge. The protocol can be optimized as needed by prompting the user for various inputs (i.e., for changing the dilution of the sample, the amount of reagent provided to the liquid sample, altering an incubation time or MAA time, or altering the NMR relaxation collection parameters).

A multiplexed assay can be performed using a variety of system designs. For example, a multiplexed assay can performed using any of the following configurations: (i) a spatially-based detection array can be used to direct magnetic particles to a particular region of a tube (i.e., without aggregation) and immobilize the particles in different locations according to the particular analyte being detected. The immobilized particles are detected by monitoring their local effect on the relaxation effect at the site of immobilization. The particles can be spatially separated by gravimetric separation in flow (i.e., larger particles settling faster along with a slow flow perpendicular to gravity to provide spatial separation based on particle size with different magnetic particle size populations being labeled with different targets). Alternatively, of capture probes can be used to locate magnetic particles in a particular region of a tube (i.e., without aggregation) and immobilize the particles in different locations (i.e., on a functionalized surface, foam, or gel). Optionally, the array is flow through system with multiple coils and magnets, each coil being a separate detector that has the appropriate particles immobilized within it, and the presence of the analyte detected with signal changes arising from clustering in the presence of the analyte. Optionally, once the particles are spatially separated, each individual analyte in the multiplexed assay can be detected by sliding a coil across the sample to read out the now spatially separated particles. (ii) A microfluidic tube where the sample is physically split amongst many branches and a separate signal is detected in each branch, each branch configured for detection of a separate analyte in the multiplexed assay. (iii) An array of 96 wells (or less or more) where each well has its own coil and magnet, and each well is configured for detection of a separate analyte in the multiplexed assay. (iv) A sipper or flow through device with multiple independently addressable coils inside one magnet or inside multiple mini magnets that can be used for sequential readings, each reading being a separate reaction for detection of a separate analyte in the multiplexed assay. (v) A sipper or flow through device with multiple independently addressable wells on a plate inside one magnet or inside multiple mini magnets that can be used for sequential readings using a single sided coil that can be traversed along the plate, each reading being a separate reaction for detection of a separate analyte in the multiplexed assay. (vi) A tube containing two compartments read simultaneously, resulting in one relaxation curve which is then fit using bi-exponential fitting to produce the separate readings for the multiplexed array. (vii) A microfluidics system where each droplet of liquid is moved around individually, to produce readings for the multiplexed array. (viii) Sequential measurements using magnetic separation and resuspension requires novel binding probes or the ability to turn them on and off. This method would be used for nucleic acid analytes in which turn on/off mechanism is based mostly on melting temperature (at higher temperatures hairpin loops relax, denaturation of double strand binding), and hybridization will occur at different temperatures. (ix) Individual capillaries, each equipped with dried particles within them, allow for small volume rapid multiplexing of one small aliquot. The dried particles are spatially separated, and this spatial separation permits the MR Reader to read each capillary tube independently. (x) Binding moieties conjugated to nanoparticles are placed in a gel or other viscous material forming a region and analyte specific viscous solution. The gel or viscous solution enhances spatial separation of more than one analyte in the starting sample because after the sample is allowed to interact with the gel, the target analyte can readily diffuse through the gel and specifically bind to a conjugated moiety on the gel or viscous solution held nanoparticle. The clustering or aggregation of the specific analyte, optionally enhanced via one of the described magnetic assisted agglomeration methods, and detection of analyte specific clusters can be performed by using a specific location NMR reader. In this way a spatial array of nanoparticles, and can be designed, for example, as a 2d array. (xi) Magnetic particles can be spotted and dried into multiple locations in a tube and then each location measured separately. For example, one type of particle can be bound to a surface and a second particle suspended in solution, both of which hybridize to the analyte to be detected. Clusters can be formed at the surface where hybridization reactions occur, each surface being separately detectable. (xii) A spotted array of nucleic acids can be created within a sample tube, each configured to hybridize to a first portion of an array of target nucleic acids. Magnetic particles can be designed with probes to hybridize to a second portion of the target nucleic acid. Each location can be measured separately. Alternatively, any generic beacon or detection method could be used to produce output from the nucleic acid array. (xiii) An array of magnetic particles for detecting an array of targets can be included in a single sample, each configured (e.g., by size, or relaxation properties) to provide a distinct NMR relaxation signature with aggregate formation. For example, each of the particles can be selected to produce distinct T2 relaxation times (e.g., one set of particles covers 10-200 ms, a second set from 250-500 a third set from 550-1100, and so on). Each can be measured as a separate band of relaxation rates. (xiv) For detection of analytes of various size or magnetic particles, or aggregates of various size, a single sample with multiple analytes and magnetic particles can undergo separation in the presence of a magnetic or electric field (i.e., electrophoretic separation of magnetic particles coated with analytes), the separate magnetic particles and/or aggregates reaching the site of a detector at different times, accordingly. (xv) The detection tube could be separated into two (or more) chambers that each contain a different nanoparticle for detection. The tube could be read using the reader and through fitting a multiple exponential curve such as A*exp(T2_1)+B*exp(T2_2), the response of each analyte could be determined by looking at the relative size of the constants A and B and T2_1 and T2_2. (xvi) Gradient magnetic fields can be shimmed to form narrow fields. Shim pulses or other RF based Shimming within a specific field can be performed to pulse and receive signals within a specific region. In this way one could envision a stratification of the Rf pulse within a shim and specific resonance signals could be received from the specific shim. While this method relies on shimming the gradient magnetic field, multiplexing would include then, to rely on one of the other methods described to get different nanoparticles and the clusters to reside in these different shims. Thus there would be two dimensions, one provided by magnetic field shims and a second dimension provided by varying nanoparticle binding to more than one analyte. Nanoparticles having two distinct NMR relaxation signals upon clustering with an analyte may be employed in a multiplexed assay. In this methods, the observation that small particles (30-200 nm) cause a decrease in T2 with clustering whereas large particles (>800 nm) cause an increase with clustering. The reaction assay is designed as a competitive reaction, so that with the addition of the target it changes the equilibrium relaxation signal. For example, if the T2 relaxation time is shorter, clusters forming of analyte with small particles are forming. If on the other hand, the T2 relaxation becomes longer, clusters of analyte with larger particles are forming. It's probably useful to change the density/viscosity of the solution with additives such as trehalose or glucose or glycerol to make sure the big particles stay in solution. One nanoparticle having binding moieties to a specific analyte for whose T2 signal is decreased on clustering may be combined with a second nanoparticle having a second binding moiety to a second analyte for whose T2 signal is increased on clustering. In the case for which the sample is suspected to have both analytes and the clustering reaction may cancel each other out (the increased clustering cancels the decreased clustering), one could envision an ordering of the analysis, i.e. addition of competitive binding agents to detect a competitive binding and thus T2 signal that would be related to the presence/absence of the analyte of interest in the sample. Alternatively, if the increased clustering cancels the decreased clustering in this multiplexing format, one could envision use of different relaxation pulse sequences or relaxation determinants to identify the presence/absence or concentration of analyte in the sample. (xvii) Precipitation measurement of particles. In this method, multiple types of particles designed to capture different target sequences of nucleic acid are designed So that the particle size is small enough that the particles bound with analyte remain suspended in solution. Sequential addition of an “initiator” sequence that is complementary to a nucleic acid sequence conjugated to a second set of particles (a larger particle, not necessarily having magnetic properties) and contains a complementary sequence to the captured target DNA sequence. After hybridization, clusters will form if the target DNA sequence is present, e.g. the magnetic nanoparticle conjugated with probe anneals to one specific sequence on the target analyte and the other particle binds to another sequence on the target nucleic acid sequence. These clusters will be big enough to precipitate (this step may require a centrifugation step). In the same reaction, and simulataneously, one could design an additional magnetic particle, second particle set to anneal with a second nucleic acid sequence for which formation of the magnetic nanoparticle-analyte-second particle clusters do not precipitate. In this way sequential addition of particles can result in differential signaling. (xvii) One possible different detection technique includes phase separated signals, which would stem from differing RF coil pulse sequences that are optimized for the conjugated nanoparticle-analyte interaction. Optimally, this could be achieved with multiple coils in an array that would optimize the ability of the different RF pulses and relaxation signal detection to be mapped and differentiated to ascertain the presence/absence of more than one analyte. Multiplexing may also employ the unique characteristic of the nanoparticle-analyte clustering reaction and subsequent detection of water solvent in the sample, the ability of the clusters to form various “pockets” and these coordinated clusters to have varying porosity. For example, linkers having varying length or conformational structures can be employed to conjugate the binding moiety to the magnetic nanoparticle. In this way, more than one type of cluster formed in the presence of an analyte could be designed having the ability of differing solvent water flow, and thus relaxation signal differences, through the aggregated nanoparticle-analyte-nanoparticle formation. In this way, two or more linker/binding moiety designs would then allow for detection of more than one analyte in the same sample. (xviii) The methods of the invention can include a fluorinated oil/aqueous mixture for capturing particles in an emulsion. In this design one hydrophobic capture particle set and an aqueous capture set are used, the hydrophobic capture particle set is designed to bind and aggregate more readily in an hydrophobic environment, whereas the aqueous capture particle set is designed to bind and aggregate in an aqueous environment. Introduction of an analyte containing sample having specific analytes that will bind to either the hydrophobic or aqueous particle, and subsequent mixing in the detection tube having both hydrophobic and aqueous solvents, binding and clustering would then result in a physical separation of analytes to either the aqueous or hydrophobic phase. The relaxation signal could be detected in either solution phase. In the event that the analytes and nanoparticles designed in this manner are physically found in an emulsion created by the mixing of the hydrophobic/aqueous phases, relaxation curves would be distinguishable in the emulsion phase. The detection tube may have a capsular design to enhance the ability to move the capsules through an MR detector to read out the signal. Further, additional use of a fluorescent tag to read out probe identity may be employed, i.e. in the case of two different analytes in the same aqueous or hydrophobic phase, the addition of a fluorescent tag can assist determination of the identify of the analyte. This method is amenable in samples for which limited isolation or purification of the target analyte away from the other material in the sample because the described resonance signals are independent of sample quality. Further, the addition of the fluorescent tag can be added in much higher concentrations that usually added in typical fluorescent studies because these tags will never interfere with the relaxation measurements. In this method, oligonucleotide capture probes that are conjugated to the magnetic nanoparticles are designed so that specific restriction endonuclease sites are located within the annealed section. After hybridization with the sample forming nanoparticle-analyte clusters, a relaxation measurement then provides a base signal. Introduction of a specific restriction endonuclease to the detection tube and incubation will result in a specific reduction of the nanoparticle/analyte cluster after restriction digestion has occurred. After a subsequent relaxation measurement, the pattern of signal and restriction enzyme digestion, one can deduce the target. (xix) In a combined method, a magnetic nanoparticle is conjugated with two separate and distinct binding moieties, i.e. an oligonucleotide and an antibody. This nanoparticle when incubated with a sample having both types of analytes in the sample will form nanoparticle-analyte complexes, and a baseline T2 relaxation signal will be detectable. Subsequent addition of a known concentration of one of the analytes can be added to reduce the clustering formed by that specific analyte from the sample. After known analyte addition a subsequent T2 relaxation signal is detected and the presence/absence of the sample analyte can be surmised. Further, a second analyte can be added to compete with the analyte in the sample to form clusters. Again, after a subsequent T2 relaxation signal detection the presence/absence of the second sample analyte can be surmised. This can be repeated.

Broadly a multiplexed assay employing the methods of this invention can be designed so that the use of one non-superparamagnetic nanoparticle to generate clusters with analyte from a sample, will reduce the overall Fe²⁺ in assay detection vessel and will extend the dynamic range so that multiple reactions can be measured in the same detection vessel.

Multiplexing nucleic acid detection can make use of differing hybridization qualities of the conjugated magnetic nanoparticle and the target nucleic acid analyte. For example, capture probes conjugated to magnetic nanoparticles can be designed so that annealing the magnetic nanoparticle to the target nucleic acid sequence is different for more than one nucleic acid target sequence. Factors for the design of these different probe-target sequences include G-C content (time to form hybrids), varying salt concentration, hybridization temperatures, and/or combinations of these factors. This method then would entail allowing various nucleic acid conjugated magnetic nanoparticles to interact with a sample suspected of having more than one target nucleic acid analyte. Relaxation times detected after various treatments, i.e. heating, addition of salt, hybridization timing, would allow for the ability to surmise which suspected nucleic acid sequence is present or absent in the sample.

Use complimentary amplicons to block one reaction and allow serial hybridizations. In this method, universal amplification primers are used to amplify more than one specific nucleic acid sequence in the starting sample, forming an amplicon pool. Specific oligonucleotide conjugated to magnetic nanoparticles are added to the sample and a relaxation measurement is taken. The sample is then exposed to a temperature to melt the oligonucleotide-analyte interaction and addition of a oligonucleotide that is not attached to a magnetic nanoparticle is added to compete away any analyte binding to the magnetic nanoparticle. A second magnetic nanoparticle having a second oligonucleotide conjugated to it is then added to form clusters with a second specific target nucleic acid analyte. Alternatively, the method could have a step prior to the addition of the second magnetic nanoparticle that would effectively sequester the first magnetic nanoparticle from the reaction vessel, i.e. exposing the reaction vessel to a magnetic field to move the particles to an area that would not be available to the second, or subsequent reaction.

Each of the multiplexing methods above can employ a step of freezing the sample to slow diffusion and clustering time and thus alter the measurement of the relaxation time. Slowing the diffusion and clustering of the method may enhance the ability to separate and detect more than one relaxation time Each of the multiplexing methods above can make use of sequential addition of conjugated nanoparticles followed by relaxation detection after each addition. After each sequential addition, the subsequent relaxation baseline becomes the new baseline from the last addition and can be used to assist in correlating the relaxation time with presence/absence of the analyte or analyte concentration in the sample.

Hidden capture probes. In this method of multiplexing, oligonucleotides conjugated to the magnetic nanoparticles are designed so that secondary structure or a complementary probe on the surface of the particle hides or covers the sequence for hybridization initially in the reaction vessel. These hidden hybridization sequences are then exposed or revealed in the sample vessel spatially or temporally during the assay. For example, as mentioned above, hybridization can be affected by salt, temperature and time to hybridize. Thus, in one form of this method, secondary or complementary structures on the oligonucleotide probe conjugated to the magnetic nanoparticle can be reduced or relaxed to then expose or reveal the sequence to hybridize to the target nucleic acid sample. Further, secondary structures could be reduced or relaxed using a chemical compound, e.g., DMSO. Another method to selectively reveal or expose a sequence for hybridization of the oligonucleotide conjugated nanoparticle with the target analyte is to design stem-loop structures having a site for a restriction endonuclease; subsequent digestion with a restriction endonuclease would relax the stem-loop structure and allow for hybridization to occur. Alternatively, a chemical cut of the stem-loop structure, releasing one end could make the sequence free to then hybridize to the target nucleic acid sequence.

Where the multiplexed array is configured to detect a target nucleic acid, the assay can include a multiplexed PCR to generate different amplicons and then serially detect the different reactions.

The multiplexed assay optionally includes a logical array in which the targets are set up by binary search to reduce the number of assays required (e.g., gram positive or negative leads to different species based tests that only would be conducted for one group or the other).

The systems of the invention can run a variety of assays, regardless of the analyte being detected from a bodily fluid sample. A protocol dependent on the identity of the cartridge unit being used can be stored on the system computer. In some embodiments, the cartridge unit has an identifier (ID) that is detected or read by the system computer, or a bar code (1D or 2D) on a card that then supplies assay specific or patient or subject specific information needed to be tracked or accessed with the analysis information (e.g., calibration curves, protocols, previous analyte concentrations or levels). Where desired, the cartridge unit identifier is used to select a protocol stored on the system computer, or to identify the location of various assay reagents in the cartridge unit. The protocol to be run on the system may include instructions to the controller of the system to perform the protocol, including but not limited to a particular assay to be run and a detection method to be performed. Once the assay is performed by the system, data indicative of an analyte in the biological sample is generated and communicated to a communications assembly, where it can either be transmitted to the external device for processing, including without limitation, calculation of the analyte concentration in the sample, or processed by the system computer and the result presented on a display readout.

For example, the identifier may be a bar code identifier with a series of black and white lines, which can be read by a bar code reader (or another type of detector) upon insertion of the cartridge unit. Other identifiers could be used, such as a series of alphanumerical values, colors, raised bumps, RFID, or any other identifier which can be located on a cartridge unit and be detected or read by the system computer. The detector may also be an LED that emits light which can interact with an identifier which reflects light and is measured by the system computer to determine the identity of a particular cartridge unit. In some embodiments, the system includes a storage or memory device with the cartridge unit or the detector for transmitting information to the system computer.

Thus, the systems of the invention can include an operating program to carry out different assays, and cartridges encoded to: (i) report to the operating program which pre-programmed assay was being employed; (ii) report to the operating program the configuration of the cartridges; (iii) inform the operating system the order of steps for carrying out the assay; (iv) inform the system which pre-programmed routine to employ; (v) prompt input from the user with respect to certain assay variables; (vi) record a patient identification number (the patient identification number can also be included on the Vacutainer holding the blood sample); (vii) record certain cartridge information (i.e., lot #, calibration data, assays on the cartridge, analytic data range, expiration date, storage requirements, acceptable sample specifics); or (viii) report to the operating program assay upgrades or revisions (i.e., so that newer versions of the assay would occur on cartridge upgrades only and not to the larger, more costly system).

The systems of the invention can include one or more fluid transfer units configured to adhere to a robotic arm (see FIGS. 43A-43C). The fluid transfer unit can be a pipette, such as an air-displacement, liquid backed, or syringe pipette. For example, a fluid transfer unit can further include a motor in communication with a programmable processor of the system computer and the motor can move the plurality of heads based on a protocol from the programmable processor. Thus, the programmable processor of a system can include instructions or commands and can operate a fluid transfer unit according to the instructions to transfer liquid samples by either withdrawing (for drawing liquid in) or extending (for expelling liquid) a piston into a closed air space. Both the volume of air moved and the speed of movement can be precisely controlled, for example, by the programmable processor. Mixing of samples (or reagents) with diluents (or other reagents) can be achieved by aspirating components to be mixed into a common tube and then repeatedly aspirating a significant fraction of the combined liquid volume up and down into a tip. Dissolution of reagents dried into a tube can be done is similar fashion.

A system can include one or more incubation units for heating the liquid sample and/or for control of the assay temperature. Heat can be used in the incubation step of an assay reaction to promote the reaction and shorten the duration necessary for the incubation step. A system can include a heating block configured to receive a liquid sample for a predetermined time at a predetermined temperature. The heating block can be configured to receive a plurality of samples.

The system temperature can be carefully regulated. For example, the system includes a casing kept at a predetermined temperature (i.e., 37° C.) using stirred temperature controlled air. Waste heat from each of the units will exceed what can be passively dissipated by simple enclosure by conduction and convection to air. To eliminate waste heat, the system can include two compartments separated by an insulated floor. The upper compartment includes those portions of the components needed for the manipulation and measurement of the liquid samples, while the lower compartment includes the heat generating elements of the individual units (e.g., the motor for the centrifuge, the motors for the agitation units, the electronics for each of the separate units, and the heating blocks for the incubation units). The lower floor is then vented and forced air cooling is used to carry heat away from the system. See FIGS. 44A and 44B.

The MR unit may require more closely controlled temperature (e.g., ±0.1° C.), and so may optionally include a separate casing into which air heated at a predetermined temperature is blown. The casing can include an opening through which the liquid sample is inserted and removed, and out of which the heated air is allowed to escape. See FIGS. 45A and 45B. Other temperature control approaches may also be utilized.

The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how the devices, systems, and methods described herein are performed, made, and evaluated, and are intended to be purely exemplary of the invention and are not intended to limit the scope of what the inventors regard as their invention.

EXAMPLE 1 Candida Assay

In the assay used for Candida, two pools of magnetic particles are used for detection of each Candida species. In the first pool, a species specific Candida capture oligonucleotide probe is conjugated to the magnetic particles. In the second pool, an additional species-specific capture oligonucleotide probe is conjugated to the magnetic particles. Upon hybridization, the two particles will hybridize to two distinct species-specific sequences within the sense strand of the target nucleic acid, separated by approximately 10 to 100 nucleotides. (Alternatively, the two capture oligonucleotides can be conjugated to a single pool of particles, resulting in individual particles having specificity for both the first and second regions). The oligonucleotide-decorated magnetic particles are designed to aggregate in the presence of nucleic acid molecules from a particular species of Candida. Thus, unlike the inhibition assays used for creatinine and tacrolimus, the Candida assay features an increase in agglomeration in the presence of the target Candida nucleic acid molecules. The hybridization-mediated agglomerative assay architecture is depicted in FIG. 32.

Carboxylated magnetic particles are used in the Candida assays. Magnetic particles were conjugated to oligonucleotide capture probes to create oligonucleotide-particle conjugates. For each target amplicon, two populations of oligonucleotide-particle conjugates were prepared. Oligonucleotide-particle conjugates were prepared using standard EDC chemistry between aminated oligonucleotides and carboxylated particles, or, optionally, by coupling biotin-TEG modified oligonucleotides to streptavidin particles. Coupling reactions were typically performed at a particle concentration of 1% solids.

Post-conjugation, functional oligonucleotide densities were measured by hybridizing Cy5-labeled complements to the particles, washing the particles three times to remove non-hybridized oligo; and eluting by heating to 95° C. for 5 minutes. The amount of Cy5 labeled oligonucleotide was quantified via fluorescence spectroscopy.

The coupling reactions were performed at 37° C. overnight with continuous mixing using a rocker or roller. The resulting particle conjugates were washed twice with 1× reaction volume of Millipore water; twice with 1× reaction volume of 0.1 M imidazole (pH 6.0) at 37° C. for 5 minutes; three times with 1× reaction volume of 0.1 M sodium bicarbonate at 37° C. for 5 minutes; then twice with 1× reaction volume of 0.1 M sodium bicarbonate at 65° C. for 30 minutes. The resulting particle conjugates were stored at 1% solids in TE (pH 8), 0.1% Tween®20).

The panel of Candida species detected includes C. albicans, C. glabrata, C. krusei, C. tropicalis, and C. parapsilosis. The sequences are amplified using universal primers recognizing highly conserved sequence within the genus Candida. The capture oligonucleotides were designed to recognize and hybridize to species-specific regions within the amplicon.

An aliquot of a blood sample was first subjected to lysis as follows:

(i) A whole blood sample was mixed with an excess (1.25×, 1.5×, or 2×) volume of ammonium chloride hypotonic lysis solution. Addition of lysis solution disrupts all RBCs, but does not disrupt WBC, yeast, or bacteria cells. The cellular matter was centrifuged at 9000 rpm for 5 minutes and lysate was removed. Intact cells were reconstituted with 100 μl TE (tris EDTA, pH=8) to a final volume of about 100 μl; and

(ii) To the approximately 100 μl sample, 120 mg of 0.5 mm beads were added. The sample was agitated for 3 minutes at about 3K rpm, thereby forming a lysate.

An aliquot of ca. 50 μl of lysate was then subjected to PCR amplification by addition of the lysate to a PCR master mix including nucleotides; buffer (5 mM (NH₄)SO₄,3.5 mM MgCl₂, 6% glycerol, 60 mM Tricine, pH=8.7 at 25° C.; primers (forward primer in 4× excess (300 mM forward; 0.75 mM reverse) to allow for asymmetric single strand production in the final product); and thermostable polymerase (HemoKlenTaq (New England Biolabs)). After an initial incubation at 95° C. for 3 minutes, the mixture is subjected to PCR cycles: 62° C. annealing; 68° C. elongation; 95° C.—for 40 cycles. Note: there is a 6° C. difference in the annealing and elongation temperatures; the annealing and elongation may be combined into a single step to reduce the total amplification turn-around time.

The PCR amplicon, now ready for detection, is combined with two populations of particles in a sandwich assay.

The PCR primers and capture probes which can be used in the Candida assay are provided below in Table 2.

TABLE 2 PCR Primers Pan Candida- PCR Forward GGC ATG CCT GTT TGA GCG TC (SEQ ID NO. 1) Primer Pan Candida- PCR Reverse GCT TAT TGA TAT GCT TAA GTT CAG CGG GT (SEQ ID NO. 2) Primer Capture Probes Candida albicans Probe #1 ACC CAG CGG TTT GAG GGA GAA AC (SEQ ID NO. 3) Candida albicans Probe #2 AAA GTT TGA AGA TAT ACG TGG TGG ACG TTA (SEQ ID NO. 4) Candida krusei Probe #1 CGC ACG CGC AAG ATG GAA ACG (SEQ ID NO. 5) Candida krusei Probe #2 AAG TTC AGC GGG TAT TCC TAC CT (SEQ ID NO. 6) Candida krusei probe AGC TTT TTG TTG TCT CGC AAC ACT CGC (SEQ ID NO. 32) Candida glabrata Probe #1 CTA CCA AAC ACA ATG TGT TTG AGA AG (SEQ ID NO. 7) Candida glabrata Probe #2 CCT GAT TTG AGG TCA AAC TTA AAG ACG TCT G (SEQ ID NO. 8) Candida parapsilosis/ AGT CCT ACC TGA TTT GAG GTC NitInd¹AA (SEQ ID NO. 9) tropicalis Probe #1 Candida parapsilosis/ CCG NitInd¹GG GTT TGA GGG AGA AAT (SEQ ID NO. 10) tropicalis Probe #2 Candida tropicalis AAA GTT ATG AAATAA ATT GTG GTG GCC ACT AGC (SEQ ID NO. 33) Candida tropicalis ACC CGG GGGTTT GAG GGA GAA A (SEQ ID NO. 34) Candida parapsilosis AGT CCT ACC TGA TTT GAG GTC GAA (SEQ ID NO. 35) Candida parapsilosis CCG AGG GTT TGA GGG AGA AAT (SEQ ID NO. 36) inhibition control 5′ GG AAT AAT ACG CCG ACC AGC TTG CAC TA (SEQ ID NO. 37) inhibition control 3′ GGT TGT CGA AGG ATC TAT TTC AGT ATG ATG CAG (SEQ ID NO. 38) 1. NitInd is 5′5-Nitroindole, a base that is capable of annealing with any of the four DNA bases. 2. Note that oligo Ts are added as spacers

Optionally, the assay is carried out in the presence of a control sequence, along with magnetic particles decorated with probes for confirming the presence of the control sequence.

EXAMPLE 2 Diagnostic Candida Panel

Testing was performed over the course of 45 days. C. albicans and C. krusei reference strains as well as C. albicans clinical isolates were cultivated and maintained for the duration of the study.

Materials:

C. albicans and C. krusei nanoparticles: Two particle populations were generated for each species, the particles bearing covalently conjugated to oligos complementary to species-specific sequences within the ITS2 region (see Example 14). The particles were stored at 4-8° C. in TE (pH 8), 0.1% Tween and were diluted to 0.097 mM Fe in DNA hybridization buffer immediately before use.

Candida strains: Panels were performed using C. albicans reference strain MYA 2876 (GenBank FN652297.1), C. krusei reference strain 24210 (GenBank AY939808.1), and C. albicans clinical isolates. The five C. albicans isolates used were cultivated on YPD at room temperature. Single colonies were selected, washed 3 times with PBS, and then quantified via hemocytometer for preparation of whole blood spikes. The samples were stored as frozen glycerol stocks as −80° C.

Human whole blood: Whole blood was collected from healthy donors and treated with K₂EDTA and spiked with washed serially diluted Candida cells at concentrations spanning 1E5 to 5 cells/mL. Cell spikes prepared in fresh blood were stored at −20° C.

Erythrocyte Lysis buffer: A hypotonic lysis buffer containing 10 mM potassium bicarbonate, 155 mM ammonium chloride, and 0.1 mM EDTA was filter sterilized and stored at room temperature prior to use. Alternatively an erythrocyte lysis agent can be used, such as a non-ionic detergent (e.g., a mixture of Triton-X 100 and igepal, or Brij-58).

PCR master mix: A master mix containing buffer, nucleotides, primers, and enzyme was prepared (20 μL 5× reaction buffer, 22 μL water, 2 μL 10 mM dNTP, 3 μL 10 μM forward primer, 3 μL 2.5 μM reverse primer, 10 μL HemoKlenTaq, and 40 μL bead beaten lysate) and stored at room temperature.

Particle hybridization master mix: A master mix consisting of nanoparticle conjugates, salts, surfactant, and formamide was prepared (78 μL formamide, 78 μL 20×SSC, 88.3 μL 1×TE+0.1% Tween, 7.5 μL CP 1-3′, and 8.2 μL CP 3-5′) immediately before use.

Glass beads (0.5 mm), used in mechanical lysis of Candida, were washed in acid and autoclaved and stored at room temperature prior to use.

PCR Protocol:

A general scheme of the workflow for detection of a pathogen (e.g., Candida) in a whole blood sample is shown in FIG. 47. The protocol was as follows: (i) human whole blood spiked samples were allowed to warm to room temperature (−30 minutes); (ii) 1 mL of erythrocyte lysis buffer was aliquoted into each tube; (iii) each tube was centrifuged at 9000 g for 5 minutes and the lysed blood discarded; (iv) 100 μL of 0.2 micron filtered TE was aliquoted into each tube; (v) 120 mg of acid washed glass beads were added to each tube; (vi) each tube was vortexed for 3 minutes at maximum speed (3000 rpm); (vii) 50 μL of lysed sample was aliquoted into a tube containing PCR master mix (viii) cycle PCR reactions as follows: (initial denaturation: 95° C., 3 minutes; 30-40 cycles at 95° C., 20 seconds; 30-40 cycles at 62° C., 30 seconds; 30-40 cycles at 68° C., 20 seconds; final extension: 68° C., 10 minutes; final soak: 4° C.); (ix) each of the samples was briefly centrifuged after thermocycling to form pellet clotted blood; (x) 5 μL of particle master mix was aliquoted into the tube for every 10 μL of amplified sample; (xi) the resulting mixture was well mixed and the sample denatured at 95° C. for 3 minutes; (xii) the sample was hybridized at 60° C. for 1 hour with gentle agitation; (xiii) the sample was then diluted to 150 uL with particle dilution buffer, and equilibrated to 37° C. in a heat block for 1 minute; and (xiv) the T₂ of the sample was measured using a T₂ MR reader.

Test Results

Repeatability of Candida albicans detection in human whole blood: To determine the repeatability of the T₂ measurement on C. albicans infected human whole blood, we conducted an eight day study in which the same donor spiked and amplified sample was hybridized to the superparamagnetic particles (n=3) each day and the resulting T₂ values were recorded.

The within run precision is shown in FIG. 46A and in general is tight with the CV's of all measurands less than 12%. The repeatability observed over the course of eight days is shown in FIG. 46B with the CVs less than 10% across the range of Candida concentrations and 6% for the negative control. Importantly, a two population two-tailed Student's T-test was applied to determine if the difference in means between the mock Candida infected blood at 10 cells/mL and the healthy donor blood was significant. The results are summarized in Table 3.

TABLE 3 The difference in means between 10 cells/mL infected blood and negative control is significant (p value <0.0001) P value <0.0001 Are means signif. different? (P < 0.05) Yes One- or two-tailed P value? Two-tailed t, df t = 40.69 df = 23 Number of pairs 24 Mean of differences 287.7 95% confidence interval 273.0 to 302.3 R square 0.9863

Influence of sample matrix on Candida albicans and Candida krusei detection and reproducibility: Healthy blood from 6 donors was spiked with a range of C. albicans or C. krusei cells (1E5 cells/mL to 0 cells/mL). From the Candida albicans spiked blood, sixteen independent experiments were conducted. Each experiment consisted of PCR amplification of the 1E5 to 0 cells/mL spiked blood with each amplification reaction subjected to three replicate T₂ detection experiments; thus for C. albicans a total of 48 T₂ values were recorded at each tested concentration (see FIG. 48A). At the lowest test concentration (10 cells/mL), we failed to detect Candida albicans 37% of the time (6 out of 16 experiments); however at 100 cells/mL Candida albicans was detected 100% of the time. This suggests the LOD for C. albicans is above 10 cells/mL but below 100 cells/mL. More concentrations will be tested between the 10 CFU to 100 cells/mL to better define the LOD; however we do not expect to observe any major matrix effects on assay performance. This is evidenced by the CVs of the T₂ measurements which are as follows: 12.6% at 1E5 cells/mL in 6 donor bloods, 13.7% at 1E4 cells/mL, 15% at 1E3 cells/mL, 18% at 1E2 cells/mL, and 6% at 0 cells/mL. This suggests the assay can robustly detect at C. albicans concentrations greater than or equal to 100 cells/mL with no major inhibition of performance introduced through the donor blood samples.

The same experiment was conducted using a reference strain of C. krusei. In this case 7 independent experiments were conducted as the remaining spiked blood was reserved for blood culture analysis. We did not detect at 10 cells/mL in any of the experimental runs but detected at 100 cells/mL for all experimental runs. This suggests the LOD between 10 and 100 cells/mL. Again a titration of cell concentrations between 100 and 10 cells/mL will need to be conducted to better define the LOD. The CV's of the measurements across the range of concentrations was: 10.5% at 1E5, 9% at 1E4, 12% at 1E3, 20% at 1E2, 6.4% at 10, and 5.2% at 0 cells/mL. The results are shown in FIG. 48B.

Preliminary determination of limit of detection: Five Candida albicans clinical isolates were spiked into 6 different donor blood samples at concentrations of 1E4, 1E3, 5E2, 1E2, 50, 10, 5, and 0 cells/mL. Each isolate was spiked into a minimum of two different donor blood samples. Amplification reactions were detected via T₂ measurement with the results plotted in FIG. 49. It is important to note that no data was removed for cause within this study. We did not detect C. albicans 50% of the time at 5 cells/mL or 10 cells/mL; however at 50 cells/mL C. albicans was detected 95% of the time. These data were generated using different clinical isolates; each isolate contains a different number of rDNA repeats and the number of these repeats can vary as much as 4-fold from strain to strain (i.e. ˜50 units to 200 units). Since the input target copy numbers will vary slightly from strain to strain and certainly from species to species, there will be subtle differences in the absolute T₂ values observed at very low cell numbers (i.e., 10 cells/mL). Based on our very preliminary study, the data suggests a cut-off of 10 cells/mL; however this determination cannot be made in the absence of final formulations of reagents as well as the instrument/cartridge. It does suggest that defining the C5-C95 interval will be difficult because at 10 cells/mL each reaction contains only 4 cells. Titrating at cell numbers lower than this becomes challenging with this input volume of blood. Using the Poisson distribution to calculate the number of reactions that would contain 0 cells at 10 cells/mL indicates only 2% of the reactions would not contain cells; however at 5 cells/mL, 13% of the reactions will contain no Candida cells, and at 2 cells/mL, ˜37% of the reactions would not contain Candida cells. To increase the assay's sensitivity to 95% at 10 cells/mL, we could increase the amount of lysate added to the PCR reactions from 40 μL to 50 μL and increase the amount of patient blood from 400 μL to 800 μL/reaction.

Preliminary determination of sensitivity/specificity: Initially, quantification of input Candida colony forming units was conducted using a hemocytometer; however in this case the operator counted budding daughter cells as separate cells. As our data is reported in colony forming units/mL and not cells/mL, buds should not be quantified. Because of this error, fewer cells/mL of Candida are present at the various spike concentrations and our sensitivity at 10 cells/mL was only 90%, while our specificity was 100%. At 25 cells/mL or greater we observe 100% sensitivity and 100% specificity. In all cases, blood culture vials inoculated with Candida cells were blood culture positive by day 8. It should be noted that the default setting for blood culture is incubation for 5 days; however we needed to extend this incubation time as many of our inoculums required >5 days incubation. As an example, Table 4A shows the time from inoculation to culture positive recorded for four different C. albicans clinical isolates inoculated into blood culture.

The results of T₂ measurements conducted on 800 μL aliquots from these spiked whole blood samples is shown in Table 4B. In all cases we were able to detect at 25 cells/mL, or greater, however we were unable to detect clinical isolate C3 at 12 cells/mL. It is important to note the CFU's were quantified via hemocytometer and not Coulter counter for this particular method compare experiment. In total 51 blood culture bottles were inoculated with hemocytomer quantified Candida albicans clinical isolates and 35 negative blood culture vials were included in the experiment. The results for inoculums greater than 25 cells/mL are shown in the contingency table in Table 5.

TABLE 4A Time to blood culture positive results for 4 different Candida albicans clinical isolates. C. albicans isolate 100 CFU/mL 25 CFU/mL 12 CFU/mL 0.0 0.0 C1 161 hrs +/− 12  161 hrs +/− 12 161 hrs +/− 12 192 hrs 192 hrs C2 40 hrs +/− 12  65 hrs +/− 12 47.5 hrs 192 hrs 192 hrs C3 69.5 hrs 161 hrs +/− 12 161 hrs +/− 12 192 hrs 192 hrs C4 40 hrs +/− 12 43 hrs 47.5 hrs 192 hrs 192 hrs *Note: all blood culture negative vials were negative and discarded at t = 8 days

TABLE 4B T₂ values obtained following PCR amplification and T2 detection on the pre-culture in vitro spiked blood samples shown above (assay time ~3 hrs). C. albicans isolate 100 CFU/mL 25 CFU/mL 12 CFU/mL 0.0 0.0 C1 739.0 409.0 632.5 112.7 112.8 C2 983.2 1014.5 997.6 117.4 114.8 C3 912.7 510.5 113.3 116.2 112.0 C4 807.6 741.2 665.2 119.1 115.9 T2 values (in msec) are the mean n = 3 with CV's less than 10% for replicate measurements

TABLE 5 Contingency Table used to calculate sensitivity/specificity at >25 cells/mL C. albicans. Positive 51 (true positive)  0 (false positive) 51 (TP + FP) Negative  0 (false negative) 35 (true negative) 35 (FN + TN) Total 51 (TP + FN) 35 (FP + TN) 86 (N) Estimated Sensitivity = 100 × [TP/(TP + FN)] = 100% (95% confidence interval = 93 to 100%) Estimated Specificity = 100 × [TN/(FP + TN] = 100% (95% confidence interval = 90 to 100%)

Standardization of CFU quantification has improved our assay sensitivity and reproducibility. Preliminary results from 27 blood culture bottles are shown in Table 6. These preliminary results indicate we have 100% sensitivity and specificity at 10 cells/mL or greater. We have additionally begun method comparisons using C. krusei. Preliminary results (from 36 vials) are shown in Table 7. The results indicate we have a sensitivity/specificity of 88%/100% at 10 cells/mL or greater and 100% sensitivity/100% specificity at 33 cells/mL or greater for Candida krusei. Another important change which was instituted prior to the new blood culture agreement comparisons was the employment of a multi-probe particle. In this case the T₂ clustering reactions for C. albicans detection were conducted using albicans/parapsilosis/tropicalis multi-functional particles while C. krusei was detected using the glabrata/krusei multi-functional particles.

TABLE 6 Contingency Table used to calculate sensitivity/specificity at >10 cells/mL C. albicans. Positive 18 (true positive) 0 (false positive) 18 (TP + FP) Negative  0 (false negative) 6 (true negative)  6 (FN + TN) Total 18 (TP + FN) 6 (FP + TN) 24 (N) Estimated Sensitivity = 100 × [TP/(TP + FN)] = 100% (95% confidence interval = 81.4 to 100%) Estimated Specificity = 100 × [TN/(FP + TN] = 100% (95% confidence interval = 54 to 100%)

TABLE 7 Contingency Table used to calculate sensitivity/specificity at >10 cells/mL Candida krusei. Positive 24 (true positive) 0 (false positive) 24 (TP + FP) Negative  3 (false negative) 9 (true negative) 12 (FN + TN) Total 27 (TP + FN) 9 (FP + TN) 36 (N) Estimated Sensitivity = 100 × [TP/(TP + FN)] = 89% (95% confidence interval = 71 to 98%) Estimated Specificity = 100 × [TN/(FP + TN] = 100% (95% confidence interval = 66 to 100%)

Preliminary assessment of clinical accuracy: Clinical accuracy is defined as the ability to discriminate between two or more clinical states, for example Candidemia versus no Candidemia. Receiver Operator Characteristic (ROC) plots describe the test's performance graphically illustrating the relationship between sensitivity (true positive fraction) and specificity (true negative fraction). The clinical accuracy (sensitivity/specificity pairs) is displayed for the entire spectrum of decision levels. Using the data generated from the 10 cells/mL and 50 cells/mL clinical isolate spiked whole blood samples, two ROC plots were generated and are shown in FIGS. 50A and 50B. The area under the curve is often used to quantify the diagnostic accuracy; in this case our ability to discriminate between a Candidemic patient with an infection of 10 cells/mL or 50 cells/mL versus a patient with no Candidemia. At 10 cells/mL the area under the curve is 0.72 which means that if the T₂ assay was run on a randomly chosen person with Candidemia at a level of infection of 10 cells/mL, there is an 72% chance their T₂ value would be higher than a person with no Candidemia. The clinical accuracy of the test is much higher at 50 cells/mL with the area under the curve at 0.98. Again indicating that in a person with Candidemia at this level of infection, the T₂ assay would give a value higher than a sample from a patient without Candidemia 98% of the time. This is excellent clinical accuracy for infection levels of 50 cells/mL. ROC plots were not prepared for the 100 cells/mL samples or higher as the area would be translating to 100% clinical diagnostic accuracy. Final clinical accuracy is determined from real patient samples on the clinical platform.

Assay turnaround time: The primary assay steps with estimated times are: (i) hypotonic lysis/centrifugation/bead beating (8 min); (ii) PCR (120 min); (iii) hybridization of amplicon to particles (30 min); (iv) hMAA (10 min.); and (v) transfer and read (10 sec.). The processing time for the assay is estimated at ˜178 minutes (˜3 hrs), excluding reagent and equipment preparation. This is the workflow used for qualification; however we have demonstrated that the following modified work-flow with shorter PCR and hybridization steps does yield the same detection sensitivity (see FIG. 51) (albeit with a reduction in the amount of amplicon generated for some Candida species (i.e., glabrata) and hence a smaller delta T₂ between diseased and normal): (i) hypotonic lysis/centrifugation/bead beating (8 min); (ii) PCR (70 min); (iii) hybridization of amplicon to particles (30 min); (iv) hMAA (10 min); and (v) transfer and read (10 sec.). This modified flow generates a TAT of 133 minutes or 2 hours and 13 minutes (and this is without migration to a faster thermocycler).

Conclusions

This testing demonstrates a current T₂ based molecular diagnostic assay for Candidemia with the following metrics: (i) detection of Candida albicans within whole blood at a range spanning 5-1E5 cells/mL (5-log); (ii) detection of Candida krusei within whole blood at a range spanning 10 cells/mL to 1E5 cells/mL; (iii) sensitivity/specificity of 100%/100% at >25 cells/mL; (iv) diagnostic accuracy of greater than 98% for concentrations >50 cells/mL; (v) assay compatibility with whole blood (no major matrix effects observed using twelve different donor blood samples); (vi) repeatability of T₂ measurements (less than 12% within the same day and less than 13% across eight days); and (vii) reduced total assay turnaround time to 2 hours 3 minutes.

We have tested higher input volumes of human blood and found that efficient hypotonic lysis is achievable with these larger blood volumes; further it has increased the reproducibility of detection at 10 cells/mL.

Contamination was observed within 2 samples of the 50 titrations. To reduce contamination issues, the PCR steps may be separated from the detection steps. Further, chemical/biochemical methods may be used to render the amplicons unamplifiable. For example, uracils may be incorporated into the PCR product, and a pre-PCR incubation may be conducted with uracil N glycosylase.

The advantages of the systems and methods of the invention include the ability to assay whole blood samples without separating proteins and non-target nucleic acids from the sample. Because no losses in target nucleic acids are incurred through DNA purification (e.g., running Qiagen column after lysis and prior to amplification results in >10× loss in sensitivity; and use of whole blood interferes with optical detection methods at concentrations above 1%), sample-to-sample variability and biases (which can be introduced by DNA purification) are minimized and sensitivity is maximized.

Over 10% of septic shock patients are carriers of Candida; this is the third most prevalent pathogen after S. aureus & E. coli, and there is an approximately 50% mortality rate for septic shock patients infected with Candida. Candida is the fourth leading cause of hospital acquired infections. Rapid identification of these patients is critical to selecting proper treatment regimens.

EXAMPLE 3 Viral Assay

CMV genomic DNA was spiked into CMV-free healthy donor blood samples, 40 μL of this spiked blood was aliquoted into a 100 μL total volume PCR reaction. Amplification was conducted using a whole blood compatible thermophilic DNA polymerase (T2 Biosystems, Lexington, Mass.) and exemplary universal primers that were designed as follows: 24 mer end-C6 linker-CMV specific sequence, the exact sequences were as follows:

(SEQ ID NO. 11, universal tail probe #1) 5′-CAT GAT CTG CTG GAG TCT GAC GTT A-3′, (SEQ ID NO. 12, universal tail probe #2) 5′-GCA GAT CTC CTC AAT GCG GCG-3′, (SEQ ID NO. 13, CMV US8 forward primer) 5′-CGT GCC ACC GCA GAT AGT AAG-3′, and (SEQ ID NO. 14, CMV US8 reverse primer) 5′-GAA TAC AGA CAC TTA GAG CTC GGG-3′.

The primers were designed such that the capture probes (i.e., the nucleic acid decorating the magnetic particle) would anneal to the 10 mer region (10 mers are different on either 5′ or 3′ end). The final primer concentration in the reaction tube was 300 nM and PCR master mix which included 5 mM (NH₄)₂SO₄, 3.5 mM MgCl₂, 6% glycerol, 60 mM Tricine (pH 8.7)). Five separate sample reaction tubes were set up. Cycle PCR reactions followed an initial denaturation of 95° C. for 3 minutes, and each cycle consisted of 95° C., 20 seconds; 55° C., 30 seconds; and 68° C., 20 seconds. At 30, 33, 36, 39, and 42 cycles reaction tubes were removed and maintained at 4° C. Once all samples were ready, 5 μL of particle master mix (6×SSC, 30% formamide, 0.1% Tween) was aliquoted into the tube for every 10 μL of amplified sample; the resulting mixture was well mixed and the sample denatured at 95° C. for 3 minutes; the sample was hybridized at 45° C. for 1 hour with gentle agitation; the sample was then diluted to 150 μL with particle dilution buffer (PBS, 0.1% Tween, 0.1% BSA), placed into a temperature controlled hMAA magnet for 10 minutes, and equilibrated to 37° C. in a heat block for 1 minute; and the T₂ relaxation time for each of the five separate samples was measured using a T₂ MR reader (see FIG. 52).

The primers were designed to allow the magnetic particles decorated with capture probes to anneal to the 10 mer region (10 mers are different on either 5′ or 3′ end), providing particles with a universal architecture for aggregation with specific amplification primers.

The results provided in FIG. 52 show that the methods and systems of the invention can be used to perform real time PCR and provide quantitative information about the amount of target nucleic acid present in a whole blood sample.

EXAMPLE 4 Real-Time PCR

Previous results showed that when particles were present in the PCR reaction the amplicon production was inhibited. We hypothesize that moving the particles to the side of the reaction tube during the thermocycling will allow production of amplicon. A simple magnetic separator/PCR block insert (FIG. 53) was designed to keep nanoparticles on the side walls during PCR reaction, thus minimizing interference and particle exposure to the PCR reaction components. Upon removal of the magnetic field, particles can be completely resuspended into the reaction mixture.

In one experiment, we tested the rate at which particles could be sequestered to the side of the tube and returned to solution. In this experiment, 100 μL of the C. albicans (3′ and 5′) particle mix in 1×TE (˜150 msec unclustered T2 baseline) went three times through clustering/unclustering process at 95° C. This was followed by the following protocol

1. vortex, incubate at 37° C. for 1 min, measure T2;

2. heat at 95° C. for 5 min on the magnetic PCR insert;

3. incubate at 37° C. for 1 min, measure T2;

4. vortex 15 sec, incubate at 37° C. for 1 min, measure T2; and

5. go to step 2.

The results of this experiment are shown in Table 8 below.

TABLE 8 cycle # 1 2 3 4 tube 1 147.1 150.8 154.9 140.9 T2 unclustered 2198.6 1965.6 2161.4 T2 clustered at 95°C. % T2 incr. 1494.2 1303.5 1395.1 avrg. % 1397.6 tube 2 143.5 147.4 150.4 144.2 T2 unclustered 2240.7 2141.3 2086.5 T2 clustered at 95°C. % T2 incr. 1561.4 1452.9 1386.9 avrg. % 1467.1

As shown in Table 8, fully reversible nanoparticle clustering was demonstrated at 95° C. when using the tested magnetic separator. Particles are stable at 95° C. for at least 3 clustering/unclustering cycles.

We next tested PCR efficiency in the presence of nanoparticles in reaction solution. PCR was performed under two conditions: (1) nanoparticles are fully dispersed in solution; and (2) nanoparticles are concentrated on the PCR test tube side walls using magnetic insert.

Three PCR reactions (with nanoparticles concentrated on the test tube wall; fully dispersed in solution; and no nanoparticles) were set up using C. albicans genomic DNA as a starting material. Successful target DNA amplification was validated using gel electrophoresis. Capture-probe decorated Seramag particles were used.

Asymmetric (4:1) PCR reactions were setup using pre-made PCR mix and 100 copies of genomic C. albicans DNA as a starting material. C. albicans capture particle mix (3′ and 5′) in 1×TE was added to reactions (1) and (3) (baseline ˜150 msec). Control reaction (2) did not have nanoparticles added (FIG. 54).

No difference was observed in PCR product formation when nanoparticles were present in solution (dispersed in solution or concentrated on test tube side walls via magnetic field) during PCR. Therefore, nanoparticles modified with capture probes do not interfere with PCR. Comparable amounts of product were generated in the reactions with and without nanoparticles present in solution as evidenced by gel electrophoresis. Also, magnetic concentration of nanoparticles on test tube side walls during PCR process does not have an effect on the PCR.

EXAMPLE 5 Internal Controls for C. Albicans

A variety of impurities and components of whole blood can be inhibitory to the polymerase and primer annealing. These inhibitors can lead to generation of false positives and low sensitivities. To assure that clinical specimens are successfully amplified and detected, the assay can include an internal control nucleic acid that contains primer binding regions identical to those of the target sequence. The target nucleic acid and internal control are selected such that each has a unique probe binding region that differentiates the internal control from the target nucleic acid. The internal control can be an inhibition control that is designed to co-amplify with the nucleic acid target being detected. Failure of the internal inhibition control to be amplified is evidence of a reagent failure or process error. Universal primers can be designed such that the target sequence and the internal control sequence are amplified in the same reaction tube. Thus, using this format, if the target DNA is amplified but the internal control is not it is then assumed that the target DNA is present in a proportionally greater amount than the internal control and the positive result is valid as the internal control amplification is unnecessary. If, on the other hand, neither the internal control nor the target is amplified it is then assumed that inhibition of the PCR reaction has occurred and the test for that particular sample is not valid.

The already amplified and detected Candida albicans sequence was examined for use in generating an internal control. The universal primer sequences were removed from the 5′ and 3′ ends. The residual internal sequence was subjected to a random sequence generator and a random sequence was generated. The universal primer sequences were replaced at the ends and the full internal control sequence was cloned into pCR2.1-TOPO and was sequence verified.

In designing these internal controls, the following criteria and features for use in diagnostic PCR assays were employed: 1) the target and internal control DNA share the same primers; 2) the internal control and target DNA are easily distinguishable (i.e. different capture probes); 3) the amplification efficiencies of the target and internal control have been tested and are acceptable; 4) the source of the internal control is a plasmid DNA carrying the cloned internal control sequence; 5) the internal control is detected by sequence dependent hybridization; 6) the internal control plasmid is highly purified; 7) the concentration of the internal control is determined by titration; 8) the internal control plasmid is added to the PCR mix to ensure equal distribution to all of the PCR tubes; 9) it has been determined the amount of internal control in the assay reaction tubes is 100-1000 copies/reaction and this concentration has been determined to be the lowest amount that still elicits a signal via amplification. See Hoofar et al., J. Clin. Microbiol. 42:1863 (2004).

The internal inhibition control for the Candida assay was designed to co-amplify with the Pan Candida PCR primers and contain a unique intervening sequence of similar length and base composition as the Candida species. The intervening sequence was developed by applying a sequence randomizing algorithm to the C. ablicans amplicon sequence. Four randomized sequences were then thermodynamically and bioinformatically characterized. A nucleotide megaBLAST search was conducted for each sequence using both the human genomic+transcript database as well as the nr database. No significant alignments were identified with the four query sequences in either database. Each sequence was then subjected to UNAfold analysis to determine the extent of secondary structure present at the hybridization concentration of monovalent cation (600 mM) at a temperature of 60 degrees C. Two sequences were excluded at this point due to the presence of extensive stems under these hybridization conditions. Two were further characterized to determine if capture probes could be designed complementary to the 5′ and 3′ ends of the strand amplified in excess that would be devoid of poly-G tracts, and have low probabilities of forming homo and heterodimers. One sequence met all the criteria and was ordered as a PAGE purified synthetic oligonucleotide and its respective complement from IDT Technologies (Coralville, Iowa). The sequence of the internal control that will be amplified in excess is:

(SEQ ID NO. 15) 5-GGC ATG CCT GTT TGA GCG TCC TGC ATC ATA CTG AAA TAG ATC CTT CGA CAA CCT CGG TAC ACT GGG AAC AAG GCC TCA AAC ATT GAT GCT CGA CTA CAC GTA GGG CAATGC GTC TTG CTA GAA GCG AAA TCT GTG GCT TGC TAG TGC AAG CTG GTC GGC GTA TTA TTC CAA CCC GCT GAA CTT AAG CAT ATC AAT AAG CA-3.

The annealed complementary sequence is:

(SEQ ID NO. 16) 5- GCT TAT TGA TAT GCT TAA GTT CAG CGG GTT GGA ATA ATA CGC CGA CCA GCT TGC ACT AGC AAG CCA CAG ATT TCG CTT CTA GCA AGA CGC ATT GCC CTA CGT GTA GTC GAG CAT CAA TGT TTG AGG CCT TGT TCC CAGTGT ACC GAG GTT GTC GAA GGATCT ATT TCA GTA TGA TGC AGG ACG CTC AAA CAG GCATGC CA -3.

5 uM of the annealed duplex in 2×SSC was sent to SeqWright for subcloning and sequencing. The annealed duplexes contain 3′ adenosine overhangs to facilitate cloning into a TA cloning vector. This construct was cloned into pCR2.1-TOPO. Upon transformation, 5 clones were selected and sequenced to confirm the presence of the correct insert. Upon verification of the correct cloned insert, the mini-prepped plasmid DNA should be digested with EcoRV and HindIII and the insert subcloned into pBR322. From this transformation, 5 transformants were selected and the insert verified via sequencing. Two E. coli hosts bearing the pBR322-IC were frozen in 30% glycerol+LB amp. A plasmid maxi-prep was conducted using the Qiagen and yieldied ˜1 mg of purified plasmid DNA.

Capture probes were designed to hybridize nested to the Pan Candida PCR primer sequences. A 3′ aminated capture probe with a T-9 linker was designed to complementary to the 5′ end of the strand amplified in excess. A 5′ aminated capture probe with a C12 T-9 linker was designed complementary to the 3′ end of the strand amplified in excess. These sequences are shown below:

(SEQ ID NO. 17) GGT TGT CGA AGG ATC TAT TTC AGT ATG ATG CAG-TTT TTT TTT-3′Amino (SEQ ID NO. 18) 5′Amino-C12-TTT TTT TTT- TGG AAT AAT ACG CCG ACC AGC TTG CAC TA

The predicted melting temperatures (Allawi, 1997) were 75 and 78° C., respectively.

EXAMPLE 6 Candida Assay and Clinical Data

A rapid, accurate, and reproducible molecular diagnostic test was developed for the detection of five Candida species directly within human whole blood with a limit of detection (LOD) of 10 cells/mL and a time to result of less than 2 hours. The assay's clinical performance was determined using 32 blinded clinical specimens and in this study we observed 100% positive and 100% negative agreement with blood culture while accurately identifying the causative Candida species within 100% of the candidemic patient samples. We further applied the assay to blood specimens drawn from Candida positive patients and observed a decrease in Candida detection concordant with the time course of antifungal treatment. This diagnostic method is rapid, amenable to automation, and offers clinicians the opportunity to detect multiple human pathogens within complex biological specimens.

Magnetic Resonance Relaxometer

A compact magnetic resonance (MR) system was designed and constructed for precise T2 relaxation measurements in order to perform the intended assay under the described conditions. This system was held at 37° C. via temperature control and contains a samarium cobalt permanent magnet of approximately 0.5 T, corresponding to a proton frequency of operation of 22-24 MHz. All standard MR components: radio frequency probe, low-noise pre-amplifier and transmitter electronics, spectrometer board, as well as the temperature control hardware are packaged in the system. The system uses standard AC power input and connects to an external computer via Ethernet. A user friendly graphical user interface allows users to set experimental parameters.

The system has been designed to accept samples in standard 0.2 ml PCR tubes. The electronics as well as the coil were optimized to improve the measurement precision of the applicable sample volumes, allowing us to achieve single-scan run to run CVs in T2 of less than 0.1%. Instrument to instrument variability is under 2% with minimal tolerance requirements on the system components and without calibration.

Nanoparticle Sensor Conjugation and Characterization

800 nm carboxylated iron oxide superparamagnetic particles, consisting of numerous iron oxide nanocrystals embedded in a polymer matrix including a total particle diameter of 800 nm (see Demas et al., New J. Phys. 13:1 (2011)), were conjugated to aminated DNA oligonucleotides using standard carbodiimide chemistry. DNA-derivatized nanoparticles were stored at 4° C. in 1×Tris-EDTA (pH 8), 0.1% Tween-20. Iron concentration of nanoparticle conjugates were measured by dissolving the particle with 6M HCl followed by addition of hydroxylamine hydrochloride and 1,10 O-phenanthroline and subsequent spectrophotometric detection as described in Owen et al., J Immunol Methods, 73:41 (1984). Oligonucleotide derivatized particles are then subjected to a functional performance test by conducting hybridization induced agglomeration reactions using diluted synthetic oligonucleotide targets identical in sequence to the fungal ITS2 sequences from the five different Candida species within a sodium phosphate hybridization buffer 4×SSPE (600 mM NaCl, 40 mM sodium phosphate, 4 mM EDTA). Reversibility of the agglomeration reaction was confirmed by subjecting agglomerated reactions to a 95° C. heat denaturation step, conducting a T2 measurement, and repeat hybridization at 60° C. followed by a second T2 measurement.

PCR Primer and Nanoparticle Capture Probe Design

Universal Pan Candida PCR primers were designed complementary to 5.8S and 26S rRNA sequences that amplify the intervening transcribed spacer 2 (ITS2) region of the Candida genome. A pair of oligonucleotide capture probes was designed complementary to nested sequences at the 5′ and 3′ end respectively of the asymmetrically amplified PCR product. The capture probe that hybridizes to the 5′ end of the amplicon was 3′ aminated while the capture probe that hybridizes to the 3′ end of the amplicon was 5′ aminated. A poly-T linker (n=9 to 24) is added between the amino group and the first nucleotide base of the capture probe sequence. HPLC purified PCR primers and capture probes were procured from IDT Technologies (Coralville, Iowa).

Inhibition Control Design

A PCR inhibition control was designed to co-amplify with the Candida species and monitor factors within the whole blood specimens that inhibit PCR amplification. A synthetic template was designed to contain 30 nucleotide flanking sequences identical in sequence to the 5.8S and 26S regions of the Candida rRNA operon. The internal sequence within this template consists of a randomly scrambled C. albicans amplicon. Capture probes were designed complementary to the strand amplified in excess within the asymmetric Candida PCR reactions. Synthetic oligonucleotide ultramers were procured from IDT (Coralville, Iowa) identical in sequence to the inhibition control. The oligonucleotides were annealed at a concentration of 5 μM in 2×SSC and cloned into HindIII/EcoRV digested pBR322 (NEB, Ipswich, Mass.) using standard methods. Transformation was conducted via electroporation of 1 μL of the ligation reaction into electrocompetant E. coli K12 cells and the transformants were plated onto Luria Bertani (LB) agar plates containing 100 μg/mL ampicillin Two ampicillin resistant colonies were selected and cultivated in 2 mL LB ampicillin media. Plasmid mini-preps were conducted followed by restriction enzyme mapping to confirm the clones contained the correct insert. Sanger dideoxy sequencing was then conducted (SeqWright, Houston, Tex.) to confirm successful cloning of the control and DNA maxi-preps were conducted on correct insert bearing clones. Titrations of the inhibition control in the presence of increasing concentrations of all 5 species of Candida were conducted to determine the lowest concentration of inhibition control that could be reproducibly detected. Confirmation of the function of the inhibition control was demonstrated by conducting PCR reactions in the presence of titrations of known PCR interferents (SDS, heparin, ethanol) and demonstrating that amplification of the control was inhibited.

Candida Cultivation and In-Vitro Spiked Sample Preparation

MYA-2876, ATCC 2001, ATCC 24210, ATCC 66029, and ATCC 22019 were the C. albicans, C. glabrata, C. krusei, C. tropicalis, and C. parapsilosis laboratory reference strains (ATCC, Manassas, Va.) used to prepare the in-vitro spiked whole blood specimens. Yeasts were cultivated on yeast peptone dextrose agar plates (YPD) and incubated at 25° C. Single colonies were selected and suspended in phosphate buffered saline (PBS). The species were verified via ITS2 sequencing at Accugenix (Newark, Del.). The cells were then subjected to a low speed centrifugation (3000 g for 2 minutes) and washed three times with fresh PBS. An aliquot of the PBS washed cells was then diluted in ISOTON II diluent (Beckman Coulter, Brea, Calif.) within a 20 mL Accuvette and cells were quantified on a Multisizer 4 Coulter Counter (Beckman Coulter, Brea, Calif.) following the manufacturers instruction. Cells were then serially diluted to concentrations ranging from 500 to 5 cells/100 μL PBS buffer. Fresh human healthy donor blood drawn by sterile collection in K2EDTA vacutainer tubes (BD Diagnostics, Franklin Lakes, N.J.) was obtained from ProMedX. Typically five milliliters of human blood was spiked with 100 μL of quantified Candida cells. Whole blood spiked samples are then used immediately in the assay.

Whole Blood PCR

Erythrocyte lysis was conducted within 1 mL of the whole blood sample using previously described methods (see Bramley et al., Biochimica et Biophysica Acta (BBA)-Biomembranes, 241:752 (1971) and Wessels J M, Biochim Biophys Acta., 2:178 (1973)), a low speed centrifugation is then conducted and the supernatant was removed and discarded. One hundred uL of Tris EDTA (TE) buffer pH 8.0 containing 1500 copies of the inhibition control was then added to the harvested pellets and the suspension was subjected to mechanical lysis (see Garver et al., Appl. Microbiol., 1959. 7:318 (1959); Hamilton et al., Appl. Microbiol., 10: 577 (1962); and Ranhand, J. M., Appl. Microbiol., 28:66 (1974)). Fifty μL of lysate was then added to 50 μL of an asymmetric PCR master mix containing a deoxynucleotides, PCR primers and a whole blood compatible thermophilic DNA polymerase (T2 Biosystems, Lexington, Mass.). Thermocycling was conducted using the following cycle parameters: heat denaturation at 95° C. for 5 minutes, 40 cycles consisting of a 30 second 95° C. heat denaturation step, a 20 second 62° C. annealing step, and a 30 second 68° C. elongation step, and a final extension at 68° C. for 10 minutes.

Hybridization Induced Agglomeration Assays

Fifteen microliters of the resulting amplification reaction was aliquoted into 0.2 mL thin walled PCR tubes and incubated within a sodium phosphate hybridization buffer (4×SSPE) with pairs of oligonucleotide derivatized nanoparticles at a final iron concentration of 0.2 mM iron per reaction. Hybridization reactions were incubated for 3 minutes at 95° C. followed by 30 minutes incubation at 60° C. within a shaking incubator set at an agitation speed of 1000 rpm (Vortemp, LabNet International). Hybridized samples are then placed in a 37° C. heating block to equilibrate the temperature to that of the MR reader for 3 minutes. Each sample is then subjected to a 5 second vortexing step (3000 rpm) and inserted into the MR reader for T2 measurement.

Candida Patient Sample Collection Protocol.

Blood specimen discards that had been drawn in K2EDTA vacutainers (BD) on the same day as specimens drawn for blood culture (T=0) were obtained from the clinical hematology laboratory at the Massachusetts General Hospital (MGH) or Houston University Hospital. Specimens were collected and catalogued from patients having blood culture positive results. Samples were stored within the original vacutainer at −80° C. and the blinded specimen collection was shipped overnight on dry ice to T2 Biosystems. Clinical sample collection protocols were reviewed by the appropriate Human Research Committees.

Statistical Analyses

For each species, the limit of detection was determined with the use of probit modeling. For each species, the 90% level of detection and 95% fiducial intervals were calculated. Each raw T2 signal was transformed as T2_msec over the assay's background. SAS v. 9.1.3 (Cary, N.C.) was used in the statistical calculations for the analyses for limit of detection, agreement of spiked specimens with culture, sensitivity and specificity in clinical specimens, and serial assays to measure Candida clearance.

Agreement of T2 MR Detection of Candida with Blood Culture

The current gold standard for Candida diagnosis is blood culture. In vitro spiked healthy donor whole blood specimens were prepared using laboratory reference strains for C. albicans and C. krusei and clinical isolates of C. albicans at concentrations of 0, 33, and 100 cells/mL. Pediatric BACTEC blood culture vials (BACTEC Peds Plus/F vials, Beckton Dickenson) were inoculated with an aliquot of the in-vitro spiked specimens evaluated by T2MR. Blood culture vials inoculated with Candida cells were blood culture positive by day 8 in all cases. In total, 133 blood culture bottles were inoculated with 90 Candida spiked blood samples (inoculum of 33 cells/mL) or 43 negative blood samples. Ninety eight percent positive agreement and 100% negative agreement was observed between T2MR and blood culture.

Clinical Specimen Data

K2 EDTA whole blood patient specimens were obtained to test the clinical performance of the T2MR Candida assay. The patients presented with symptoms of septicemia and blood was drawn for culture. Blood sample retains were stored at 4° C. in the hematology lab and selected for T2MR if the outcome was blood culture positive for Candida, blood culture positive for bacteremia, or blood culture negative to better represent the spectrum of samples that would be run on the platform. Fourteen of the samples were from candidemic patients, eight were from bacteremic patients, and ten were from blood-culture negative patients. FIG. 57 shows the measured T2 values for all 32 patient samples. A single PCR reaction was conducted using 1 mL of each specimen. 750 copies of the internal inhibition control were added to each PCR reaction. Among Candida negative samples the average internal control (IC) signal was 279 ms with a CV across the 18 Candida negative specimens of 25%. In no cases was the IC signal below the decision threshold (128 ms, 5 standard deviations added to the mean T2 measured in Candida negative detection reactions) suggesting that all negatives were true negatives and no inhibitory substances were present with the whole blood samples. The detection reactions were multiplexed based on IDSA guidelines, such that three results were reported as follows: C. albicans or C. tropicalis positive; C. krusei or C. glabrata positive; and C. parapsilosis positive. The average T2 measured in the Candida negative specimens is 114 ms, the CV for these measurements was 2.4%, and the decision threshold (calculated by addition of five times the standard deviation measured in the Candida negative detection reactions plus the mean T2 measured in Candida negative specimens) was 128 ms. In specimens positive for Candida, the IC signal was suppressed due to competition for the amplification reagents. In instances of high C. albicans, some cross-reactivity was observed for detection with the C. parapsilosis particles (e.g. patient sample #3) however this signal is not significantly above the cut-off (20 ms) and does not lead to a difference in antifungal therapy as both C. albicans and C. parapsilosis are susceptible to fluconazole.

T2MR successfully identified fourteen samples of C. albicans, C. parapsilosis, or C. krusei which were confirmed positive by blood culture followed by the Vitek 2 biochemical card. Furthermore, the detection was specific for Candida spp. as bacteremic patient samples with Escherichia coli, Enterococcus sp., Staphylococcus aureus, Klebsiella pneumoniae, coagulase negative Staphylococcus, or alpha hemolytic Streptococcus remained negative.

Serially drawn samples were tested from two patients who exhibited symptoms suggestive of candidemia, such as persistent fever after receiving antibiotics to demonstrate the assay's utility in monitoring Candida clearance. Blood draws for T2MR occurred the same day as blood draws for blood culture. Surveillance cultures were then drawn over a course of nine days for Patient A and over a course of five days for Patient B. FIG. 3 shows the results obtained with the T2MR method for both patients. Patient A had blood drawn for culture (t=0), was diagnosed with candidemia and administered intravenous micafungin (C. glabrata) the following day via blood culture (t=1). Whole blood specimens were tested with T2MR at t=0 days, t=3 days, t=7 days, t=8 days, t=9 days. The T2MR values obtained were 320 ms at t=0, 467 ms at t=3, 284 ms at t=7, 245 ms at t=8, and 117 ms (below cut-off) for t=9. Subsequent blood culture draws on day 3 and day 8 took 24 and 48 hours to culture positive, respectively. A series of serially drawn specimens were obtained from Patient B. C. albicans was correctly detected with T2MR on day 0 (T2=426 ms). Blood culture came up positive on day 2 with subsequent C. albicans identification. One day after the patient was administered micafungin, a sharp decrease in C. albicans T2MR was evident (T2=169 ms) and three or more days after antifungal treatment was initiated no detectable C. albicans was observed. All tests were completed in a total processing time of two hours, using a fast block PCR thermocycler and three step thermocycling procedure that was not optimized for speed.

Conclusions

We have developed and validated a whole blood T2MR Candida assay capable of detecting five clinically important species of Candida that leverages the advantages of non-optical detection to eliminate analyte purification, thus enabling enable more rapid turn-around times and more reproducible results. Asymmetric PCR was used to specifically amplify the ITS2 region of the Candida genome directly in whole blood to achieve clinically relevant detection sensitivities. A T2 detection method was developed in which two pools of oligonucleotide derivatized nanoparticles hybridize to each end of the single stranded amplicon. The amplicons thus serve as interparticle tethers and induce nanoparticle agglomeration which yields a measurable and reproducible change in the spin-spin relaxometry (T2) of the protons in water molecules. We further constructed and implemented an internal inhibition control to monitor for PCR inhibitors that may be present in the patient samples.

The assay was evaluated using reference strains and clinical isolates quantified by Coulter Counter and spiked into healthy donor whole blood. Assay repeatability was measured using C. albicans spiked blood (same sample, same operator, same instrument) over the course of 10 days and we observe CV's less than 12.8% (n=30) over the entire dynamic response range (0 to 1 E5 cells/mL). The analytical sensitivity and limit of detection of <10 cells/mL were measured for C. albicans, C. tropicalis, C. krusei, and C. parapsilosis and >10 cells/mL with 92.5% detected at 10 cells/mL for C. glabrata. Although not proven, a possible cause of the higher LoD observed in C. glabrata may be that the rDNA operon copy number is reduced in C. glabrata as compared to the other queried Candida spp since it is known that C. glabrata exists in nature as a haploid while the other Candida species are diploids. Agreement with the gold standard for Candida diagnosis was high with 98% positive and 100% negative agreement observed for 133 in vitro spiked C. albicans and C. krusei samples. It should be noted that the time to result was 2 hours for the T2 Candida test while the time to blood culture positivity was typically 2 days for C. albicans and ˜1 day (18-24 hours) for Candida krusei.

The 32 clinical specimens are similar to blood culture results. The measured T2 was above a cut-off established at five standard deviations of the T2 values measured in the Candida negative specimens added to their mean. In this case the threshold was 128 ms (n=54). In no cases did we observe inhibition of the PCR reaction, as the internal control was detected within all 32 reactions with a reduced IC signal observed in Candida positive patients and a CV of 25% (mean T2 of 279 ms) across the Candida negative specimens (n=18). The assay is highly specific for Candida detection as no cross-reactivity was observed with any of the bacteremic specimens (n=8). Candida positive specimens were accurately identified, the causative Candida spp. was accurately identified, and all within a time to answer of 2 hours.

The potential for this assay to provide a rapid detection of Candida clearance after administration of antifungal therapy was also demonstrated. Two sets of patient samples were drawn and subjected to T2MR (FIG. 3). Moderate to high T2 signals for C. glabrata were observed in patient A at day 0 and day 3 with antifungal agents administered at day 1. A decrease in C. glabrata signal was observed over subsequent days with none detectable after eight days of anti-fungal treatment. A strong C. albicans signal was measured for patient B at day 0, and a sharp decline (delta T2 of 306 ms) in T2 signal was observed one day after antifungal administration with none detectable after two days of anti-fungal treatment. Although preliminary, this data suggests the test could be used to monitor treatment effectiveness and Candida clearance in a real-time fashion.

In conclusion, we have developed a sensitive and specific test for the diagnosis of candidemia caused by the five most commonly encountered Candida species. Early clinical results were encouraging and show that rapid diagnosis and species identification is achievable and could not only facilitate early treatment with the appropriate antifungal but also provide a means to monitor Candida clearance. We anticipate that this nanoparticle-based T2MR method can be broadly applied to infectious disease diagnoses in a variety of specimen types and pathogens.

EXAMPLE 7 Candida Assay Improvements

The limit of detection for the Candida assay of Example 22 was improved by washing the pellet. 2.0 mL of whole blood was combined with 100 μL of TRAX erythrocyte lysis buffer (i.e., a mixture of nonyl phenoxy-polyethoxylethanol (NP-40) and 4-octylphenol polyethoxylate (Triton-X100)) and incubated for about 5 minutes. The sample was centrifuged for 5 minutes at 6000 g and the resulting supernatant was removed and discarded. To wash the pellet, the pellet was mixed with 200 μL of Tris EDTA (TE) buffer pH 8.0 and subjected to vortexing. The sample was again centrifuged for 5 minutes at 6000 g and the resulting supernatant was removed and discarded. Following the wash step the pellet was mixed with 100 μL TE buffer and subjected to bead beating (e.g., such as with 0.5 mm glass beads, 0.1 mm silica beads, 0.7 mm silica beads, or a mixture of differently sized beads) with vigorous agitation. The sample was again centrifuged. Fifty μL of the resulting lysate was then added to 50 μL of an asymmetric PCR master mix containing a deoxynucleotides, PCR primers and a whole blood compatible thermophilic DNA polymerase (T2 Biosystems, Lexington, Mass.). Thermocycling and hybridization induced agglomeration assays were conducted as described in Example 22 to produce T2 values characteristic of the presence of Candida in the blood sample. The assay can produce (i) a coefficient of variation in the T2 value of less than 20% on Candida positive samples; (ii) at least 95% correct detection at less than or equal to 5 cells/mL in samples spiked into 50 individual healthy patient blood samples; (iii) at least 95% correct detection less than or equal to 5 cells/mL in samples spiked into 50 individual unhealthy patient blood samples; and/or (iv) greater than or equal to 80% correct detection in clinically positive patient samples (i.e., Candida positive by another technique, such as by cell culture) starting with 2 mL of blood.

Other Embodiments

All publications, patents, and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each independent publication or patent application was specifically and individually indicated to be incorporated by reference.

While the invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modifications and this application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure that come within known or customary practice within the art to which the invention pertains and may be applied to the essential features hereinbefore set forth, and follows in the scope of the claims.

Other embodiments are within the claims. 

What is claimed is:
 1. A method for amplifying a target fungal nucleic acid in a whole blood sample, the method comprising: (a) contacting a whole blood sample suspected of containing one or more fungal cells with an erythrocyte lysis agent, thereby lysing red blood cells; (b) centrifuging the product of step (a) to form a supernatant and a pellet; (c) discarding some or all of the supernatant of step (b) and resuspending the pellet to form an extract; (d) combining said extract of step (c) with beads to form a mixture and agitating the mixture to form a lysate, said lysate containing both subject cell nucleic acid and fungal nucleic acid; and (e) providing the lysate of step (d) in a detection tube and amplifying fungal nucleic acids therein by PCR to form an amplified lysate solution; wherein ten fungal cells per milliliter of said whole blood sample is sufficient to permit amplification of said target fungal nucleic acid.
 2. The method of claim 1, wherein the amplifying of step (e) comprises amplifying a Candida nucleic acid to be detected in the presence of a forward primer and a reverse primer, each of which is universal to multiple Candida species to form a solution comprising a Candida amplicon.
 3. The method of claim 1, wherein the lysing step (a) is by detergent lysis or hypotonic lysis.
 4. The method of claim 1, wherein said amplifying step (e) comprises asymmetric polymerase chain reaction.
 5. The method of claim 1, wherein said amplified lysate solution of step (e) comprises whole blood proteins and non-target oligonucleotides.
 6. The method of claim 1, further comprising (f) detecting said amplified target nucleic acid. 